Wait a bit and see how serious their relationship gets. If they break up, go and make your move. Iffff they don't, you might consider finding someone new, which of course can be hard.
I say back off. If he's into whoever he's into (didn't follow the story...kinda lost interest), it's best to leave him be. Besides, how would you feel if someone did that to you? Stole away your lover just 'cause they thought they liked/loved them more?
The button I carry around doesn't necessarily make things EASIER...
LOL! No it's not. My friend doesn't like him but he likes her. And yes, that's happened to me like 6 times. I'm used to it. But this kid I like is different and he seems more special then all the other kids I liked.
Be his friend and be yourself. Try becoming liekk a bestfriend for him,so he knows he can trust you and stuff. Don't just pop the question off to him.xD If he starts showing the same interest in you,then ask?[:
Hope I helped.Even the slightest bit xD