I do see You-chan cheating on her and it is probably inevitable. But I think it would be an interesting plot if she cheats on him without the convince of him cheating on her.
Just him being inadequate. The relationship they have now is just her following whatever flow he's feeling and that really isn't a give-and-take relationship. Not that I'm condoning adultery or saying being inadequate/unfair is a reason to cheat but there is a reality of women cheating on their husbands.