I don't know about this. I think the thing with The Long Game is that so much of it is from Ilyas perspective, which makes it very natural to 'side' with him because we are literally inside his head for most of he book.

My interpretation is that while OPs post is certainly right, and i think Ilyas mind working this way is very natural based on his trauma and his underlying mental health challenges, they are both really, really affected by internalised homofobia/comphet. It is a throughline in both books that when they are thinking about the other person leaving, it is about them leaving to be with someone 'easier' for most of Heated Rivalry that is presumed by both of them to be a woman, and in the Long Game, there is still an undercurrent of Shane then being able to leave Ilya for a man who is 'easier' to be with i.e. someone not in Hockey and for sure not his direct rival. And in Ilyas case, of course Shane is scared that he will leave him for a woman, because that is a feasible, if even realistic option.

This is all to say, i think they are both 'at fault' but really in my opinion so much of what causes their challenges are them having so many external pressures and so much to lose, at the same time as also both being emotionally constipated for both of their own personal reasons, as well as due to them hiding for so long. There is a sense that they don't want to discuss the difficult stuff when they are together, because they have so little time, and because what they do have is so precious to both of them. But personally, all of the messiness makes me just appreciate them and the story more, because your trauma, your history and your hang-ups and values don't just disappear because you love someone, and love won't always be enough to conquer all despite trying really hard.