"Pathetic", he can't help it if he likes someone. If this was a girl having a crush on a girl she knew was straight you all would be in tears cheering her on.
When he didn't know that she was a lesbian, sure. But she's come out to him and their other friends and it's been months. At that point, letting a crush that you know will never be requited fester for that long does nothing but foster a potentially toxic environment.
Even if he was a girl pining after a straight woman, I would still have the same opinion.
Plus the whole "badmouth their relationship to their other friends when they aren't around" is what adds up to him being pathetic to me.
It takes time to let go of feelings, but sitting around thinking things like "Maybe she's bi or maybe I can make her fall for me?" aren't okay.