I'm going to break up with my girlfriend of 9 months because I feel things for another girl
What about the other girl makes you want to break up with your gf?
I know the other girl needs my support and I've dated her before.
Well sometimes your heart wants things that aren't logical. You'll have to decide for yourself to follow your heart or your brain.
I don't want to hurt my girlfriend, but I think I'm just not right for her. She should end up with a different guy,
If you really feel that way, then that's all you can really do. Just make sure you talk to her about it first. Following your heart in a relationship is exactly how it should be.