Should I be weary of him?

If he is interested in you as a ual partner, then he probably doesn't want to "just be friends". That is seen as rejection. If he is at a party where he might actually hook up with someone, he will pay attention to them rather than someone who rejected him. It appears as if he wants to make you jealous, continue trying to get you in the sack, and if that fails, at least prove (to himself to some degree) that you don't matter and that he can still get laid... of course, the very fact that you are on his mind would suggest that your rejection bothered him to some degree. Either cut it off entirely and stop hanging out at the same parties, or be prepared for this to continue for awhile.