Here's a primer:
0)"Getting back into someone's pants" is a euphemism that implies that this Matt wants to have sex with J. If he's gay, give up, it's a waste of time.

1)Self-confidence is sexy. But not all guys find this attractive, some can find it emasculating. These types are usually not worth dating. Some guys find chubby girls with glasses sexy. Don't believe all of what fashion mags tell you - fetishes exist for a reason. Maybe he finds nerdy chicks interesting, who knows?

2)Lack of self-confidence could be cute, but it usually is incredibly unsexy, not to mention it gives people the impression of a needy emotional cling-on.

3)Guys are really very much like girls. Attention works easily. Pretend to find them interesting and laugh at their jokes, ask for their opinion, but don't smother them like you're obsessed. Basically, if you would like it, chances are he would too. Respect is everything.

4)He might really just think of you as a friend. Guys like having female friends, even if said female friends are traditionally considered "unattractive". It bolsters their fragile egos.

Basically, relationships that last for long periods of time don't usually happen spontaneously. People that only enter into an official one after an extended period of friendship tend to have longer lasting ones. Why don't you find out whether you both can be friends first? It's not going to go anywhere if you can't even feel natural around him. Nobody's having any fun if they feel an incessant obligation to be interesting and charming and witty all the time.