Well I didn't take the time to read through the thread so far, but I was in a similar situation recently.
Basically, YOU HAVE TO TELL HER HOW YOU FEEL. Even if you don't think she likes you.
But then you also have to make it clear that you just want her to be happy. Even if it's not with you. I think of that move as sorta going all-in in poker. 2 things can happen from there - she's like aww you're so sweet, realizes she really likes you, and hopefully falls for you. Or she says she's happy with her current boyfriend, and then you have to be content with being just friends. If that happens, then time is the key. You just have to wait it out. There's still a possibility, so just keep showing her how much you like her and such, but don't count on anything, because you don't want your heart broken.
Also, don't try to sabotage their relationship. 9 times out of 10 it will backfire. Especially don't fight the kid or anything, it'll just make her angry with you.
EDIT: The best piece of advice I can give you is just enjoy it. It wouldn't be any fun without the chase. Lemme tell ya, girl bullsh*t gets tough, a lot tougher than that, and you just have to go with it and hope for the best.