Don't be deceitful about what you want. Be into her and show it to her. Most women have a bf, or else are married. Her bringing him up could be her way of saying I'm not into you, or that you crossing the line I am in relationship (which is an anti-slvt thing).
It's ok to cross the line.
Women bring up their boyfriends I say "Oh REALLLYY? You have a boyfriend?? It's ok, I like women who have a boyfriend, that way I know you're fine. If you were single I'd be like, what's WRONG with this chick!!!!!" As you look her over on that last line. You could go "I'd be like..." and look her over, look her over, even her behind if she's facing you, "whats WRONG with this chick!!!!" As long as it all sounds in tune for you, it's good.
Most chicks have relationships, and those that don't are not my type man. If chick has no bf, why is that?
A) She's ugly or can't get one because she's a stvck up
B) She has been dumped (women would never dump a guy and be single, they do that if they have someone already)
C) She's a hoe and has someone and not mentioning him, because she wants another guy at the same time
D) Else she's new in town, and it's fine if she is
Single ladies are not my type. Ladies that are new in town are.