This is a funny discussion, because in my opinion, Edwin would never betray Killian, I even mentioned this before, but if there's one character Edwin would take a bullet for, it's Killian, and aside from Victoria (of course), there's no other character in the game that our main character is more fond of, not even Hana or Mina or any of the main girls.
With that being said, It's not like Edwin goes out of his way to steal Mina from Killian, it's quite the opposite, Mina, after she realizes she's being constantly cheated on, and treated like garbage by her horrible soon to be ex-boyfriend, then she tries to seduce us, and with the way the situation happens, there's quite literally 0 reason to feel morally bad about it, or even feel like we're "betraying our best friend", their relationship is basically over, it's just a matter of time until Mina breaks up with him, and at no point does Edwin have ill intent when interacting with Mina or is secretly trying to win her over.
There's no "Hoes-before-bros" here, Killian fucks up so massively there's no reason to even feel bad for him during the whole situation.