After marriage she was known as Antonina Tchaikovskaya.
Little is known of Antonina before she met Tchaikovsky. Her family resided in the Moscow area. They belonged to the local gentry but lived in poverty. The family was also a highly fractious one. Tchaikovsky tells us as much in a letter he wrote his sister Alexandra Davydova during his honeymoon:
After three days with them in the country, I begin to see that everything I can't stand in my wife derives from her beginning to a completely weird family, where the mother was always arguing with the father—and now, after his death, does not hesitate to malign his memory in every way possible. It's a family in which the mother hates (!!!) some of her own children, in which the sisters are constantly squabbling, in which the only son has completely fallen out with his mother and all his sisters, etc., etc.
In a separate letter to his patroness Nadezhda von Meck he added that, in the company of his in-laws, "all nearly at daggers drawn with one another... [His] torments increased ten-fold.... I find it difficult to express ... what a terrible degree my moral agonies were reaching."
Antonina first met Tchaikovsky in 1865 at the Moscow home of a mutual friend, Anastasia Khvostova, a well-known singer. His close friend Alexei Apukhtin was staying with her, and Anastasia's brother Nikolai had been a classmate of Tchaikovsky's brother Modest at the School of Jurisprudence. Antonina was 16 at the time; Tchaikovsky was 25. He did not remember her from this meeting. She, on the other hand, reportedly held a torch for him from that time forward.
She reportedly gave up work as a professional seamstress to study music at the Moscow Music Conservatory. Tchaikovsky was one of her professors. Eventually she had to abandon her studies at that institution, probably as a result of financial troubles. She wrote to Tchaikovsky on at least two occasions in 1877, two years after she had left school. At that time she was 28, far past the age at which women of that time generally married.
By June 1877, Tchaikovsky proposed marriage, in order (according to one theory) to please his family and put any social rumors regarding his sexual proclivity to rest. He described Miliukova as "... a woman with whom I am not the least in love."
The marriage was disastrous. A permanent separation followed after only six weeks of them being together. This has traditionally been blamed in large part on Antonina's character, especially by Tchaikovsky's brother Modest in his biography of the composer. Modest describes her as a "crazed half-wit." She may have been a simpleton, a woman of common ideas and tastes, as she has been described dismissively. Responsibility for the failure of the marriage may actually lie more with Tchaikovsky than with her. "In truth," Tchaikovsky biographer Anthony Holden suggests, "Antonina was as much the right woman for Tchaikovsky as any other. It was marriage which was the wrong institution."
Moreover, Tchaikovsky and Antonina did not come to a mutual understanding before their marriage regarding Tchaikovsky's homosexuality. He might not have told Antonina that he preferred men to women. If he did tell her, she might not have understood what he meant because social conventions of the period did not allow a person to be direct about such things. Sexual matters were to be discussed with allusions and euphemisms. In such a conversation, a woman as naïve or uneducated as Antonina might literally not have known what she was hearing. She might have simply agreed to anything being said. Tchaikovsky could have convinced himself that Antonina had no problem with his sexual preferences and would not mind marital abstinence. Antonina would not have entertained the thought that such preferences as his even existed, and she probably still expected him to perform sexually for her. Mutual frustration may have been inevitable.
Especially striking from Antonina's recollections of their marriage is her apparent obliviousness to Tchaikovsky's distress. This is particularly true of the brief time they cohabited in Moscow before their separation. Tchaikovsky was falling apart mentally and emotionally. For Antonina, though, this was a period of great happiness. She writes, "I would look at him surreptitiously, so he didn't notice, and admire him enormously, especially during morning tea. So handsome, with kindly eyes which melted my heart, he breathed such freshness into my life! I would just sit there looking at him, and think 'Thank God he belongs to me and no-one else! Now he is my husband, no-one can take him away from me ...'"
Antonina's reaction once her husband took himself away from her and his brother Anatoly told her the separation would be permanent proved at least as disconcerting. Nikolai Rubinstein, who had himself met Antonina, accompanied Anatoly and promptly took charge of the situation. At Tchaikovsky's apartment, a surprised Antonina invited both men in for tea. Rubinstein spelled out the details of her husband's condition, and the report from a psychologist who had examined him. He did so with a bluntness and "cruel precision of expression," Anatoly later recalled to Nikolay Kashkin, that "made me go hot and cold."[8 ] Antonina listened meekly. She then said she would be pleased to agree to whatever her "darling Peti" wanted. She then began pouring tea. This reaction surprised both men.
Rubinstein made his excuses and left as soon as he had a chance, leaving Anatoly to discuss "more personal family matters." What happened next stunned Anatoly. "Anatonina Ivanova saw Rubinstein to the door, and returned with a broad smile on her face, saying, 'Well, who'd have thought I would entertain the famous Rubinstein to tea at my home today!'" [8 ] She then recited a litany of the many men who had fallen for her. After that she asked what Anatoly would like for dinner. Anatoly followed Rubinstein out the door as soon as he could. He headed back to St. Petersburg and made urgent arrangements to take his brother on a prolonged tour of Western Europe.
Antonina's reaction to Rubinstein and Anatoly's visit has usually been quoted as an example that, even at the beginning of her separation from Tchaikovsky, she was not healthy psychologically. This was how it was quoted long after the fact by Kashkin. It was also adapted in this context by Tchaikovsky's brother Modest, who became the composer's biographer. Another explanation is that Antonina was unable to grasp at that moment the full import of what Rubinstein had told her—let alone digest it or give any more than a conventional and respectful response.
Antonina remained convinced she was the victim of a family conspiracy to end the marriage. She wrote, "We were separated by constant whispering to Pyotr Ilyich that family life would kill his talent. At first, he paid no attention to this talk, but then he began somewhat to listen to it more and more attentively.... To lose his talent was for him the most dreadful thing of all. He began to believe their slanders and became dull and gloomy." 
In Antonina's mind, Tchaikovsky's collapse, which immediately preceded their separation, was caused by his heart being torn between her and his music. She believed it enough to accompany him to the railway station on the last day of their union. "One day, he told me he needed to go away on business for three days. I accompanied him to the mail train; his eyes were wandering, he was nervous, but I was so far in my thoughts from any trouble already hanging over my head. Before the first bell he had a spasm in his throat and went alone with jerky irregular steps to the station to drink some water. Then we entered the car, he looked at me plaintively, without lowering his eyes.... He never came back to me." 
There was a conspiracy, but not one of the kind Antonina imagined. Rather than a plan to remove her husband from her, it was one to make him appear more sympathetic in the role of victim in their marriage:
Tchaikovsky himself insisted to his patroness, Nadezhda von Meck, "My wife, whatever she may be, is not to be blamed for my having driven the situation to the point where marriage became necessary. The blame for everything lies on my lack of character, my weakness, impracticality, childishness!" He considered his falling in with her, at a time when he had decided to be married simply for the sake of being married, as something to simply attribute to Fate. Nevertheless, he personally showed nothing but disregard for her after their separation, often referring to her as The Reptile. For the rest of his life, any news concerning her drove him to hysterics. A single letter from her could upset him for several days.
He disparaged her especially to von Meck, in terms that likely dispelled any doubts his patroness had about the composer's marriage being a gross mis-match. "You will ask, of course: but how did we spend the time when she and I were alone together? She is very talkative, but all her talk comes down to the following two subjects. Hourly she would repeat to me innumerable stories about innumerable who had felt tender feelings toward her. For the most part, these were generals, nephews of prominent bankers, well-known artists, even members of the imperial family."  Whether Tchaikovsky exaggerated in this statement could be considered open to question.
"Next," he continued to von Meck, "she would no less frequently, and with a sort of inexplicable passion, describe to me the vices, the cruel and base actions and detestable behavior of all her relatives, with every of whom, it turned out, she is in enmity. Her mother would especially catch her in this.... The third topic of her tireless chatter was her stories of life at boarding school. There was no end to them."  He then offered a twin-pronged coup de grace aimed at illustrating Antonina's insensitivity while appealing to von Meck's firmly-held belief, as the mother of 11 children, in family as the sole justification for marriage. "Desiring to know what maternal instincts she had, I asked her once whether she liked children. I received in reply: 'Yes, when they are clever.'" 
Tchaikovsky was not normally so virulent toward any individual. His reasons for it were deeply personal. From his first mention of marriage to Modest, Tchaikovsky stressed the need for a woman who would allow him complete freedom in continuing his homosexual relations. He was convinced by Antonina's compliance to treat their marital relationship as one of "brotherly love" that he had found such a woman. He also saw the cultural and intellectual gap between them as an aid in this plan. A more sophisticated woman, he wrote Modest, would possibly have been less accommodating. He convinced himself that he could control Antonina because of her lack of sophistication.
Things changed when Tchaikovsky returned to Moscow from Kamenka. Antonina demanded that he fulfill his marital duties in the bedroom. Tchaikovsky considered this change an act of betrayal. It sent him into despair and severely wounded his masculine pride. Out of fairness to Antonina, however, Tchaikovsky may have deceived her by the very act of marrying her while fully aware of his sexual preference. In her eyes, it may have been he who continued to humiliate her by refusing to have sex with her.
Antonina might have regretted for the rest of her life that she ruined the chance to give Tchaikovsky a normal sex life by a lack of seductiveness on her part. As the marriage unfolded, it became obvious that either she was not persuaded by his explanations regarding his sexuality or she failed to fully comprehend what he told her. She had noticed nothing wrong in her husband's behavior when they left Moscow after their wedding. She may have concluded, wrongly, that time was on her side, that patience and perseverance would eventually make things right. For this reason she may have consented to his abstinence, at least for a time.
Due to strict regulations regarding divorce in Imperial Russia, the two remained legally married until Tchaikovsky's death. This did not mean the question of divorce was out of the question. On the contrary: the possibility arose in 1878 and 1879. Since the only legal ground for divorce was adultery, Antonina would have to perjure herself about being unfaithful. This she would not do—even, in 1878, with a 10,000-ruble incentive from von Meck. This sum would have been payable through his publisher, P.I. Jurgenson, once a divorce had been finalized. Antonina's unwillingness plus the possibility of unwanted revelations regarding Tchaikovsky's sex life may have led him to drop the matter.
Antonina may have helped fuel Tchaikovsky's fear of public exposure by her unpredictable behavior. She wrote him wild letters during her stay at Kamenka immediately following their separation. In them, she sometimes accusing him, sometimes cajoling him. In July 1880, she accused him of spreading rumors about her throughout Moscow. She also threatened the worst: "Why didn't you start with yourself, telling ... about your own terrible vice?"
However, in March 1881 Antonina gave birth to a child out of wedlock. Tchaikovsky now had legal grounds for divorce. He did not act. He might have thought that legal action would drag up matters he hoped were forgotten or at least buried. He continued to send her a regular allowance, which may have helped buy her silence. Divorce would have meant Tchaikovsky's freedom from any further financial responsibility for her. Eventually, she produced three children by (allegedly) three different fathers. She gave up all three of these children to foundling hospitals.
In later years, the couple met briefly only a couple of times, much to Tchaikovsky's displeasure. Though she outlived Tchaikovsky by 24 years, she spent the last 20 of them in an insane asylum.
After his death she wrote or dictated her reminiscence about their marriage. While they were printed in 1894 and reprinted in 1913, they were never made widely known. In this document, according to Tchaikovsky scholar Alexander Poznansky, she comes across consistently as naive, superficial and not very intelligent. She is also very coherent. This would seem to further belay the more eccentric view of her given by Modest. Her memoirs contain no trace of mental abnormality. They reveal a woman devoted to the memory of her husband, an appreciation of his greatness and the vague feeling of an enormous misunderstanding having taken place between them. "Likewise," Poznansky adds, "nothing in the reminiscences gives any grounds for suspecting them for being a forgery. On the contrary, the genuineness of the intonation, the idiosyncratic style, and the wealth of detail all attest its authenticity."