"Christians, in the bible it says, eye for eye, tooth for tooth, so if my girlfriend wills to have an abortion?"
The whole eye-for-an-eye, tooth-for-a-tooth thing was to LIMIT revenge in response to someone's trespasses against you. if someone blinds your eye, don't take their head off. If they knock out a tooth, don't rip off their jaw.
Your'e to limit the damage you inflict to be proportional to the damage inflicted on you.
and since the Bible doesn't consider a life to begin until the First Breath, then abortion isn't murder. it is a loss, and if you cause a miscarriage, you might pay a fine. But it's not a death sentence.
So, you can break up with her, especially if it's someone else's kid (because you're SUCH a good Xian, you wouldn't be the father, right), maybe fine her (if it's your kid, you filthy sinner), and refuse to pick her up at the clinic.
But no, not killing her. That's not supported biblically.