"My brother, he always hated me. And I know why, but..."
Alright, since there does not seem to be an exact reason given as to why exactly Alexei hates Ilya, let's dive into the family dynamics, shall we? Because I have thoughts and feelings, and the lack of information gives us some beautiful space for possible interpretations!
What we know:
Alexei is Ilya's older brother; he's four years older than Ilya
Irina committed suicide when Ilya was 12 and Alexei 16
Both Grigori and Alexei are part of the police
Alexei is abusing substances
Alexei has a wife and a daughter
We don't know for sure (going off show canon here) if Alexei knows that Ilya is queer. He does use a homophobic slur against him, insinuating that he might have clocked something, but at the same time it could also just him being a jerk, the same way homophobic slurs are part of the locker room talk in professional sports.
We will go through possible reasons for their animosity chronologically:
Alexei was an only child for the first four years of his life. When Ilya came along, he suddenly had to share their mother's love and their father's attention. Maybe he felt like their mother loved Ilya more, not because of anything Irina did, but it can happen so easily when another child comes along. Especially once Ilya showed a deepened interest in ice hockey, and Irina was the one to be there for all the practices, cheering him on and supporting him.
Another possibility is Irina developing postpartum depression after giving birth to Ilya. It's established that she struggled with depression, but regardless, PPD can happen to anyone. It would likely have gone untreated, too, so Alexei would always connect Ilya's death with his mother changing and turning sad. Something a child cannot possibly grasp, much less when it remains undiscussed. So, whenever Alexei looks at Ilya, he blames him for losing the mother he used to have. Or worse, for losing their mother altogether, after she committed suicide.
Alexei was older when they lost their mother. While Grigori likely wasn't ever paternal, it's still safe to assume that Ilya got slightly more care after Irina's death, because he had still been so young. Grigori felt like Ilya needed more support to stay on track, especially with him training to become a professional ice hockey player, while Alexei was well on his way to finishing school and starting work.
Alexei likely started abusing substances after their mother's death, as a coping mechanism. And chances are high that he resents Ilya for that, too, because while he's out there, having a career, earning millions, he's barely getting through each day, using substances to cope.
Alexei followed their father's footsteps, though, and it very much feels like an attempt to get his approval, after all. And culturally, he would have had the better chances to become the favourite son. His father is shown to be someone of a higher rank within the police, and Alexei could have worked his way up. Even with Ilya being successful, that likely would have gotten him equal amounts of respect, if not more (respect being a term used loosely. Never said out loud, but a shared understanding of a son who followed his father's footsteps as a symbol of respect/admirationfor him). But he failed. It's unlikely he is anything but a regular officer, with his addiction, so he ended up being a disappointment instead, and their father lets him know that, subtly, constantly. Everyone knows Alexei Rozanov is the son of Grigori Rozanov, and what a shame, what a shame. Look at the golden child, Ilya Rozanov, instead. At least he has one child who amounted to something.
If Alexei knows that Ilya is queer, or even just suspects it, it only furthers the bitterness he feels at Ilya being successful - because how dare he be a professional hockey player while also being queer? If they had been from anywhere but Russia, chances would be that he would have tried to out him out of spite, to ruin his career, but he is well aware that this would taint their father's reputation as well.
And, maybe most of all: Alexei has so many misconceptions about Ilya, because they never fucking talk. They can't be blamed for that, but on top of Alexei believing that Ilya is the golden boy, he also feels like Ilya isn't struggling at all. Which, of course, couldn't be further from the truth, but while Alexei turned to drugs, Ilya turned to his career. Pushed it all down, down, down. Hid is depression, swallowed down every heavy, heavy feeling and thought. Ilya almost broke, too, but he doesn't face that until way, way later. We, as viewers/readers, know that Ilya is not okay. But Alexei doesn't see that. All he sees is that his life fell apart after their mother died, and Ilya just moved on and became successful anyway.
And Ilya likely has a very clear and heavy understanding of how Alexei feels about his success. How he feels that, on the surface, he gets to have it all. The career, the money, the freedom from their family. The freedom from addiction. Only, it's not true. Ilya doesn't care about his career, doesn't care about the money. It is eating him alive that he can't be there for their father. It is eating him alive that his niece has to grow up the way she does. It is eating Ilya fucking alive that he has all this sadness inside of him that nobody ever fucking asks him about. Because he's the golden boy, he has it all. And he carries it all. And it's heavy, too heavy, but Alexei only ever sees what's on the surface.
Ilya understands why Alexei hates him, or at least he understands some of it. Certainly enough to add to the weight of it all, because how could he possibly tell him that he's wrong, that he would gladly give it all away, just to have their mother back again? That he would give it all away, to be able to be with the love of his life? To get rid of the darkness that threatens to swallow him whole every fucking day, every day since their mother has left them?
And Alexei might hate Ilya, in a broken, broken way, but he will never hate Ilya as much as Ilya hates himself, for making it out alive (barely, barely), while Alexei is actively drowning right in front of his eyes, and there's absolutely nothing, nothing he can do about it, nothing he can do to save him, just like there had been nothing he could have done to save their mother all those years ago.
