i'll start from the end.
the best openers are the ones that are real, or at least really intrest you.
the opener does not matter!
about how to bridge the opener to a conversation, all you need to do, is make statements or ask questions...
like after the girlfriend opener saying
you:"oh, so you don't think its cheating, so what would you consider cheating?"
her: bla bla bla
you: "oh, that is cheating! don't tell me it ever happened to you!"
her: bla bla bla bla bla
you: "okay, really quick cause i have to go soon, I once dated a girl that had really deep trust issues.. apparently her ex, cheated on her by...... bla bla bla"
deep conversation..
you know... it really doesn't matter what you say.. make them interested..
a small tip is, instead of asking questions, making statements..
if you wanna know if she is local say: "your not local, arn't you?"
this way, if you are right, you get points for being so perceptive, and if you are wrong, it becomes a regular question where she says: "actually i am from her bla bla bla..."
man! just converse.. but at the first few minutes make sure you time constraint enough and that you are locked in.
if you are locked in the set... psychologically they will want you to stay..
if you lean against the bar and they are talking to you, your welcome to stay forever...
Good luck.
Mike.