Don't get back with girl 1. She ended the relationship, and then hooked up with another guy. That is the harsh reality. Do not be suckered in to returning. If she wanted to figure things out in her life, she could have done so with you by her side. She chose not to.
To me, she sounds like a drama queen. She probably creates most of her own problems just for attention, and to get guys to come in and save her. She uses people because she doesn't know how to keep up a relationship. She probably wants you back and will try to get you back, but only when things fall through with the other guy. Leave her to suffer. She deserves it.
Girl 2 sounds like a good option. I think that she will make a much better partner. However this will destroy their friendship, giving your old girlfriend one less friend. That is a fact.
I think that girl 1 has hurt you enough bro. Get up, move on, and let her use others to fill her voids. She won't be satisfied with them, because ultimately she is not satisfied with herself. This is a her problem.
So mai gangsta fresh, find out what's behind door #2, and don't let door #1 hit your *** on the way out