Responses
If ur talking about the cousin who was adopted, then yea sorta.
Spoilers if u haven't completed:
It came from dependency. We're shown his parents neglected him since he was a kid, he ended up latching on to the kind older sister who entered his family and treated him well.
Maybe it was a crush at most, but in the end he loves her genuinely for the kindness she has shown him. Yuri is quite immature as well, but his love for her isn't shown as romantic for the most part.
is yuri in love with his sister?