I need help or advice about a girl..?

I met this girl and have been talking to her since the beginning of 9th grade (almost finished with 10th now). I've been involved with one of her good friends, dated her, we broke up, then dated again (broke up two months ago about). I'm not sure why or how, but I stopped by her house one night and we sat in the driveway and just talked, and were totally comfortable and trusting with each other. She liked me while i liked both her and her friend, but unfortunately i chose her friend (this was the first time i dated her friend, only lasted two weeks). Right after we dated then broke up for the second time (after taking a month off of talking then another 2 from liking each other) me and this girl, who considered me her best friend, got involved with each other (she was still dating one of my friends). I made the mistake of going to her house, where we had sex and the day after, she realized that she wanted to shape up for her boyfriend. I was extremely happy for her that she decided to do this, because I want to see her as happy as possible. Both of us have made our share of mistakes, and I'm glad she decided to shape up. While being happy for her, I've been feeling very strange lately, and it's unrecognizable to anything else I've felt so far....Could I get advice on what I'm feeling or what to do? Thanks in advance to anyone who can help =)I need help or advice about a girl..?
unfortunately you made a mistake of picking her friend over her. you probably would have had a great relationship. well she could still be your friend and maybe you should try to enjoy your choice you made and just try to shape up your relationship with your ex or forget them both and think of them only as friends and take a break from dating. you'll find someone else. tough situation the involvement with the one girl is a little messing up the situation but its too late now. learn from your mistakes right?I need help or advice about a girl..?
your as worried as hell and regret it YOU SHOULD HAVE LISTEN TO THOSE SEX TALKS =p
i'm guessing u still like her