Broken friendship, LONG STORY but BEST ANSWER 10 points ! I need Advice bad !?

First off it sounds like your cap friend was hurt in high school and since has matured and moved on from your leo friend, who obviously hasn't matured, her attitude towards people is what people don't like, I can understand and appriciate the fact that the two of you have been long time friends, but it sounds like she has a lot of growing up and maturing to do. You can't force your cap friend to like her and want to hang out, honestly from what you said about her, I don't think I would want to hang out with her either. She acted immaturley and inconsiderate at your birthday party, your cap friend tried avoiding the drama which she seems to start over and over, and enjoy your birthday, but your leo wouldn't let anyone enjoy it. Unfortunately, it sounds like its time to start cutting ties with your leo friend until she can grow up a bit, she's not in high school anymore so she needs to quit acting like she is, hell even the kids I went to school with didn't act that immature. Enjoy having your cap friend around and grow in that friendship, but until your leo grows up, she will continue to act this way and treat you this way. You yourself sound like a mature smart person (aside from almost starting a fist fight) why continue to hang around with someone who is only going to ruin and bring down your good times? You can still be there for her if she truely needs a good friend, but I would just slowly start removing myself until she shows some maturity.