Well, the guy was just like "Chitose met her first love and they are getting along well? She should just switch girlfriend and dump Yae".
And this is why he's the bad guy people.
He took his girlfriend for granted.
Nah what I saw is that he is one of those people he read a lots of romance manga/novel and this trope kind to happen in them. At least he shipping yuri over here, which indicates that he not hating on the LGBT+ community and some how supporters them it in a way. I just don't like it when he being keep in the dark, should at least tell you boyfriend that you don't love him anymore and breakup, before f@cking another one right after that.