Nate's shy! Nate's maybe a bit embarrassed because he was drunk and not completely sure of everything he was doing. Nate maybe doesn't know if he wants anything more serious from you....
But the truth is that stares, waves, eye contact and vibes are impossible to really read. You two should really talk (beyond small talk). The intimacy you've had together might embarrass you both, but it is also confusing the two of you about what you want together. You'll never know until you talk about it, check it out.
I don't know if you are comfortable with this, but you might invite him out with you and your roommate for dinner or a movie or something. Get into a situation where you can get more comfortable and just chat. If Nate was just looking for a one night stand, he'll refuse the invitation, if he accepts, then you two have a chance to get to know each other. Friends make much better lovers... Charlie