
Okay first off, the bartender guy's opinion is biased as hell. Of course you wouldn't want their relationship to work out, because you obviously like him. Also, I understand where he's coming from but it's not his place to try to tell him that it won't work out. Grow some balls and tell him you like him or stay out of his business.
Honestly the only annoying thing about this manga is the "he's straight but has romantic feelings for this one dude" like?? what?? First of all, Ohara keeps saying that Kawai is straight right? And thats just some of the biggest bs? It's not your position to label his sexuality, and I'm pretty sure liking someone of the same gender does not make you straight.
it is pretty much bs but kawai probably isn't attracted to men in general but just ohara so he's not gay
While you are right, you also need to understand where does it come from. Japan isn't the most LGBT+ friendly culture and even yaoi has its very homophobic moments. It also shows in the ignorance of the wide spectrum that is sexuality.
Kawai isn't hay nor he is straight he is either heteroflexible (most likely) or bi, whatever he might choose to address himself.