By how the godfather reacted, Alek was probably an illegitimate child or a child out of wedlock or a child his gather had with a woman that the family was against. Anyway, he's an outcast, either because of his lineage or because of his effeminate nature.
I mean, I know they're blood related but that doesn't mean Alek can control his feelings or that it has enough power or control over feelings of an individual. And I think Alek and Ivan's circumstance is very one-sided. That said, I don't mean that I ship Alek and Ivan, nor do I mean that I support an incestuous relationships between them. I'm just examining this possibility that maybe there was a controversial history between them.
This is all just speculation on my part because I'm very curious about why Alek is so.... bitter? Resentful? Towards Ivan. Like, what did the guy do?? Disgraced the family so bad? Why did it matter to Alek so much that his 2nd degree or 3rd degree cousin, once removed, cut his ties with the Mariano (did I this right?) Family? At least, that's how I understood it from their past talks/confrontation and flashbacks.

....???? Don't tell me Alek really had a possessive crush on Ivan when they were younger and felt betrayed when it turned out Ivan can take on male lovers all along and became bitter with jealousy when he wasn't the guys that Ivan took on as a lover? *gasp* What if Alek confessed/offered a proposition to Ivan before but Ivan rejected him?!