It sounds like you have a bunch of conflicting interests here. You want to be with her. But she's with this other guy. Have you thought about the fact that he might sense that, and that's why he's a jerk to you?
Also, could it be that the real reason that you want them to break up is just so that YOU can be with her? Could it be that you might be overreacting to his attitude because you imagine that you could be a "better" match for her?
I'm not trying to sound like a jerk, I'm just trying to bring out some points you should really think about.
It sounds like you're really not over her. And the bottom line is...
Is he a jerk to her?
If not, then it's really not your business whether they should stay together or not. This sounds like a jealousy issue for BOTH of you guys. And in the end, it's her decision.