I want to clarify two aspects of the plot - one minor, one major - which need to be taken into consideration.
Roman's and Luisa's son is called "Serjozha" throughout the film. Serjozha is the diminutive form of Sergey: the boy is named after his father's lover.
The final events pass rather quickly and are somewhat broken-up so the full narrative is far from clearly spelled-out. Let's revisit the events in the order in which they are presented in the film:
The morning after after the New Year celebration, Roman reads Sergei's letter in which he explains that he has left him: he states that he will not take Roman away from his wife and son.
As Roman is reading the letter, it is revealed that Luisa has discovered the relationship (from also reading the letter?) and verbally and physically assaults Roman.
Sergey is seen sitting on a train and his voiceover of the end of the letter continues "Please, don't come looking for me".
Roman is sitting alone on the bed in the guest-bedroom of the Moscow flat, to which he relegated Sergey when Luisa came to visit. (Shall we assume Luisa has left him?). He receives a phone call from Colonel Kuznetsov. We don't yet know the content of the call.
We abruptly cut to "One month later" as Sergey is unpacking back at drama school in Moscow. He learns that Roman came to visit him when he wasn't there, and left a letter for him.
Roman begins to read the letter, jumps up, goes to a public phone, and calls Kuznetsov.
Sergey asks how he might reach Roman. Kuznetsov informs him that he left for Afghanistan shortly after the New Year, and says "Last Monday ... Sergey, we lost him".
Sergey is seen reading the letter alone in the darkened auditorium at the drama school. Roman's voiceover continues:
"To speak and to do, to think and to live: they are not the same thing, Sergey. By the time you receive this letter, I will have left for Afghanistan. The three days that Kuznetsov gave me to consider are coming to an end. But what is there to consider? I can't choose for fear of hurting those I love. I can't divide myself any longer and belong to everyone at the same time".
Sergey is next seen at Luisa's flat in Estonia.
After this extended confrontation, Sergey visits the frozen-over lake where he and Roman swam and made love much earlier in the film, as Roman's voiceover of the letter concludes:
"Sergey, I have to choose the only place where I still feel free. The sky. Please, don't wait for me. Forget me. I shall always think of you, Sergey. Mo matter what life may bring, I will always be there with you".
These are the last words of the film.
It seems pretty clear to me that Roman committed suicide, as did Sergey's childhood friend after his sexuality was discovered and he was beaten by his father on his 13th birthday. "By the time you receive this letter" is language commonly associated with suicide notes.
If you didn't stick through the four-minute 30-second end credits, there is a final, silent scene lasting 15 seconds: the hateful Major Zverev, the first character to threaten Roman with charges of forbidden homosexual affairs punishable by five years of hard labour, is seen in the dark backseat of a car; as his face is illuminated by a match lighting his cigarette, he is smiling.
Is it possible Luisa informed on Roman, cementing what Zverev suspected for years (it also came close to discovery at Roman's and Luisa's wedding when Zverev walked in on them to tell Roman "Your wife is looking for you").
This brings up the possibility that Sergey was given two options by the Russian military:
Go to Afghanistan and commit suicide - you will be regarded as a hero, your wife will receive your pension, no one will ever know you were a homosexual. Or ...
Stay and be tried and punished for homosexual relations, found guilty, serve your time, and live out your days a pariah and your family will live in shame.
You have three days to decide.
Let's read that farewell letter again:
"The three days that Kuznetsov gave me to consider (consider what?) are coming to an end. But what is there to consider? I can't choose for fear of hurting those I love (choose death or degradation?). I can't divide myself any longer and belong to everyone at the same time".
I think it's clearly forced suicide, probably ordered by Zverev.
Oddly, Tchaikovsky seems to be Roman's favourite composer.
Tchaikovsky was rather flagrantly open about his homosexuality in Tsarist Russia. It has been theorised that Tchaikovsky was forced to commit suicide after his affair with the nephew of a nobleman, a duke, got too close to the royal family.
The duke prepared a letter to be delivered to Tsar Alexander III accusing Tchaikovsky of sexual perversion; it was first shown to Tchaikovsky's fellow alumni of the Imperial School of Jurisprudence. Eight members met in a "court of honour" lasting five hours, ending in a recommendation that Tchaikovsky commit suicide.
Tchaikovsky was dead six days later at the age of 53. One possibility is that he purposely and publicly drank a glass of unboiled water while a cholera epidemic was raging in St Petersburg, infecting himself. Theories about ingesting arsenic also exist.
This still-controversial theory caused the Russian government to remove and deny access to Tchaikovsky's letters and diaries for the past several decades, and to remove all references to the great composer's sexuality.
