First up: No girl will ever get ALL your jokes - and you shouldn't like someone based on how many jokes they get! Sure, getting most of them is a big plus, but if they don't get all of them you shouldn't kill them off for it.

Second: Don't think that just because the two girls you've found so far were taken that every girl will be. I know that it's not easy to think that there will be others, and I'm not saying there will be, I'm just saying don't cut out the possibility that you just happened to come across two girls that it just wasn't going to happen with. =x

Finally: What can you do? Well, if she has a boyfriend and they both care about each other, I think it's best to just do what you can to get by or move on. It's pretty rude to disrupt a relationship that is actually working out. Also, would you want the kind of girl who lets one boyfriend go for the next guy who convinces her to do so? I always find it terribly amusing when a guy convinces a girl to cheat on her boyfriend, then she dumps him, starts going out with the guy she cheated with and then cheats on him too - and the guy can't understand why.

If he doesn't treat her right, then uh... I dunno, a girl could probably better answer that, because I don't know how that system works. I've never liked a girl who had a boyfriend that abused her in any way without her dumping him once he did.