Should i say sorry to her or should i not?

It sounds to me like you need to find some new friends. I had a similar problem in high school where i was left out half the time and my best friend was ignoring me and started hanging out with this new chick.They hung out all the time and made me feel all alone but there wasn't much i could do about it. So instead of staying upset about it and trying to win her back i found a new friend. And she was so much more nicer and actually wanted to be my friend, the funny thing was after i started hanging out with my new friend my old friend noticed and was very very jealous. It was only then when she realized how much she was going to miss me and regret singling me out.