Girl acting weird I'm confused
OK,
So I have known this girl for about 4 years I am 17 and she is 18. Throughout the time I have known her she has been with some guy that was 2 years younger than me. Well just 12 days ago she broke up with him and was single for a few days. Then she started calling me and wanting me to hang out and I have always found her attractive. So much to the point that I strongly believe I may be in love, so I started hanging out with her. Then like 5 days later we started getting close (like we would be making out and holding each other constantly). This went on for 3 days and then on the fourth some other guy she had only met once came along then all of a sudden without a word she was going farther and farther away to the point that she won't even let me lay next to her anymore. The only thing that is really different between me and him is that he is better looking than me.for the past days after, all I have been able to do is feel depressed and hope for her to come back to me or feel so angry at the guy that I want to just knock his head off and I am not a violent guy. I don't know what to do but feel like I did something wrong.
Please help,
A guy in desperate need