I'm going to make out with a girl who came on to me but was dating someone else
What makes you want to make out with a girl who already has someone?
I wanted to see if she's worth breaking up with her boyfriend for.
You should try to resist your urges. It seems a little rude to try to cheat on your girlfriend.
What is so wrong about flirting?
Kissing and trying to push for more with a taken lady is wrong and you're helping her to cheat. You should tell her that she should break up with her boyfriend if she wants you, and then go from there.