Should I break up with my girlfriend.?

I'm 16, she's 15, we've been going out over a year, we've kissed a few times but she says she's scared, we haven't gone any further, a while ago I went on holiday for a week, and we promised each other we wouldn't drink while apart, I came back and a bit later I found out she had gone to a party, got drunk, did weed, and made out with 3 people, it took ALOT to get over but I forgave her, it was our friends party the other day and I was planning on going, but she told me she was really not happy me going and she would be really angry for weeks if I did, so, for her respect I didn't go, but then she decided to go anyway, and spend the night snuggled up to some other guy,I said, I felt just as strongly about her not going because she had already cheated on me and she had told me not to go! she still went, last night we were talking, and she explained why she didn't like me going to parties, but she couldn't understand why I felt exactly the same, I said to her, I don't like it, and I will be worried all night but I wasn't going to be harsh and stop her, then we both got invited to this party, I said no, because of her, but she went anyway, I really don't know what to do!? I love her with all my heart, but this isn't fair! what should I do? and please don't just slag her off, I do still love her :/