Being a guy, and being in one of these relationships, I must say that teenage relationships beyond friendship fail.
And, truth be told, the only reason I'm in said relationship is because she asked me out, after inhibiting a crush on me for a year. I couldn't really say no.
But I personally miss the freedom of being able to give out random hugs to my friends, and have no one get jealous or mad. I miss the freedom of being able to go to parties and having a good time because I'm tied down.
I thought once, and only once, of having sex with her. And I regret it still, honestly. I love her as much ass my teenage mind can love another teenage mind, but I'd much more rather we were just friends, and if I screwup (bound to happen =/), bye bye friendship. If I didn't go out with her, who knows what the friendship on it's own would have been like.
My diagnosis: If you have any doubts, say no. Any doubts at all. Any will do. Unless you know he's...uh...what's the term gals use...Mr. Right, I'd say "Hell no" in an instant. I learned my lesson =/