My best friend asked me out... And it turned into a Cat Fight with her and my Ex-GF.?

You have to figure out how you feel. If you still have feelings for Celeste then it's best if you're not with either of them until you decide who you want to be with. If you don't have feeling for her and only have feelings for Lindsey, explain to Celeste that she doesn't own you and you can go out with whoever you want to.