So, I really like this guy (a friend I've had for awhile now) but he's in a relationship. Normally, after I found out he had a girlfriend I would give up and move on but he has admitted to STILL having a -quoting his message- "huge crush" on me. He is so flirty and everything and its driving me insane. Because I feel awful about it (feels like I'm a side chick). What should I do about this?