I've liked this guy since last yearish and one of my best friends started dating him... Lately I've caught him starring at me and trying to talk to me. He's not a player he's actually really nice and I don't know what to do considering she's my best friend... I'm almost positive they're going to break up soon because they just act like friends except she likes him too

Bide your time. Best friends are more important than the guys who will come and go.
Talk to her. Listen. Best friends can talk, right? I wouldn't say he's been looking at you because that's too iffy. Just ask her how it's going with him, and wait, and play it slowly.

For now you stay within the boundaries of good behavior and do nothing to disrespect, or undermine your friends relationship. How old are all of you?

Yes,, talk to your friend. Even though he may be "looking" at you, does not necessarily mean he wants to break up with your friend to be with you. If it really bothers you, tell HIM that he is with your best friend and you aren't interested. Yeah,, it's that easy.