
well, it's stated that there's a FATED pair so, yes, BOTH of them felt the connection/attraction when they first met but nothing happened. the seme went away and came back when the uke was a GROWN ADULT. and that's when this story starts.
people read about ABO and seem to forget the characters have animal instincts. but they're still humans, and have reason.
well, honestly, as the uke said, the sister was a b1tch for treating her brother's feelings as shit, also why was she so enraged as she saw them together? like, her "fiance" rejected her proposal and told her he was dating her brother. like she already knew all that but treated as NOTHING because she fell in love at first sight with him and so, for being a woman, she could marry him and have a family, and the brother couldn't?
the uke was also in the wrong, because marrying the sister was his way of tormenting the poor younger seme.
but also, the seme was also acting wrong. you see, he was ALWAYS waiting for the boyfriend to reach him out first after a fight, and didn't take his feelings in consideration. after all, they're in homossexual relationship and wouldn't ever be able to marry each other.
I think marrying the sister was also a way the uke used to make the seme see the sister he loved and prioritized so much didn't reciprocate all his consideration and respect. well, the couple ended up together again and the sister is now free to live her life alone...