You're not weird alone, I think it's kinda silly
It's a thing anxious people do so that they won't get hurt in their relationship if their partner ever cheats on them or smtg
I think because the bartender told him to do so... hmmmmm
Can't he think for himself,he's not a little child
But he is kind of innocent or at least he was and he is susceptible to other people saying things to him as well like how he stays behind to do work for other people like in chapter 4. I think he's just kind of naive about dating a straight guy and he wants to make it so that Sho doesn't think "Hmm... Yeah I like girls again byeeee" On him. it's stupid, but people are stupid. You can't expect everyone to act the same when there are people who can't even speak their minds.
I don't know why people think "playing hard to get" is a good think when the person that you like — likes you back and has confessed to you. Like honey, just accept the confession and date each other. It's not that hard. Or who knows, I am the weird one, maybe.