He is being SO strange... will this even work?

Listen, this is important -- You can't have a real friendship with a guy that you have feelings for if he's dating someone else. Not until you move past your feelings. You're going to constantly feel jealous that he is talking to someone else, and the flirtation that you two share is always going to keep you hoping and hanging on. You're going to be miserable all the time, while he's going to be loving the attention he gets from both of you. DON'T DO IT.