So as it turns out, Haruki isn’t the worst one here.
Aya is chasing Sei under the guise that she would be Yoru’s replacement, thinking that she would eventually be the one Sei truly loves. She even nearly broke her own childhood friendship to chase that single minded goal to only find out that it may be nothing more than a pipe dream because it turns out that Sei, underneath all of that maturity, folds like a paper bag when it comes to Yoru, despite her protests that she didn’t wanted to be treated that way. Then we find out that Yoru pretty much knows Sei folds easily when it comes to her, and plays with her despite being married, but not out of some secret love for her, but because she can.
@Katsuramuki Most likely it’s Sei thinking that if she was a man, Yoru wouldn’t forgive her for trying to steal her away from her boyfriends.