I hurt my gf again, now what?

If you're breaking up because you don't want to hurt her again, try telling her that you don't want to do that and you know she deserves better. Don't break up with her for her own good, but maybe explain how you feel and leave some space for her to think about it. If you break up, it should be a mutual decision, not just forced on her. It will still hurt but at least that way she can feel like it was for the best and pull herself together to move on.