I am truly in love with someone and I wouldn't move away from them. If it was a once in a lifetime opportunity I would find a way to bring them with me. If they weren't willing to more I would wonder if they felt they were truly in love with me.
This is a sign of an issue with them. You need to talk to them about it. If they aren't willing to work on it, move on.
Virtually every pretty girl you meet will have a boyfriend. Be open with her and let her know how you feel. Then she will do the same. Don't play games.
That depends on what you mean by overly friendly. It might be that they feel something clicked with that person.