Quick Heated Rivalry take:
I think the root cause of Hayden and Ilya's strife is that they're jealous of each other. Not in general, but about Shane specifically.
Hayden has had YEARS of being Shane's best friend, the only guy he likes to hang out with, the one whose wife cooks bird food for him, etc. Then, all of a sudden, he finds out about Ilya, and the fear begins. Will Shane now spend all his time with his boyfriend? Will Hayden still be as important in his life?
And on Ilya's end, Hayden gets to have bits of Shane that he doesn't. Hayden can be seen with Shane out in public, and no one will blink an eye. They can be casually affectionate with each other, and it's just hockey bros. All these things that Ilya wants with Shane, Hayden already has, and a part of Ilya really doesn't want to share.
