He deemed to be the rational one in the physical relationship. He said not to get any feelings involved, that it's just sex. He doesn't want to carry the uke's emotional baggage into the relationship they have.
But without him realising it, he's starting to care more. He didn't really have to go out of his way and and give his own piece of thoughts after the meeting to that person who's dating Uke's ex-boyfriend, but he did anyway because it's affecting him to see the Uke feeling so hurt.
He went against the rule that he himself have set up, he cares, he involved feelings into the game he started. So he was just pissed at himself.
Lmao what an idiot, stop being baka mister Seme and treat our boi preciously
Why the fuck did he suddenly lash out at the end?