My girlfriend still sees her ex boyfriend.?

This one night in early February, i saw this girl for the second time at a party. Her and i talked and got really familiar with each other and became very close that night. There was little drinking, but the things that we talked about were very meaningful (life, why people love money so much and take nature for granted, etc). The party was not at a house, but at a beach - so when we talked the moonlight shined above so it was all very romantic. We kissed for the first time that night - but shortly after the kiss she told me that she had a boyfriend. I know that if i was the boyfriend, i would go crazy... But lets not get into that - but everything between her and i seemed so perfect, that preventing another kiss from happening would just be foolish. So we kissed a couple more times, and the next morning her and i talked a little (we camped at the beach) and said that we would talk more another time. So a couple days go by and i end up going to her house with one of my friends. When i was there, her and i made out a few times, and i got her phone number. The next time we saw each other was valentines day - she said that she would rather spend it with me than her boyfriend... Anyways, she ended up breaking up with her boyfriend, and a day after she did that, her and I started going out. Her ex boyfriend didnt know about me until two weeks into our relationship, and all she told him was that her and i just met. (He doesnt know about her cheating on him). She explains to me that it was really hard letting him go, but she was really glad doing it, because shes more happier with me than him - but being in a relationship for 8 months is hard to just let go of. She said that he was not only a bf, but a good friend, and she doesnt want to lose that part of him. So around the second month she explained to me that she never wants to talk to him again - cause hes a to her, calling her names and such, and how he is just stressing her out. I never said anything negative about him, only that she doesnt deserve to be called these names, and if he is stressing her out, she should just cut off the friendship. Btw, i said that i completely understood that if she wants to be friends with him. I didn't want to be the boyfriend and completely cut her off from him, because i understand that she still wanted to be friends with him. And when they broke up, she told me that she was really glad she did it, because it wasn't a really good relationship anyways - she didnt even feel like his gf. SO, for some reason, about a month ago, things between him and her seemed to get better. I dont really know how or why, but they did. So it got to a point where she wanted me to meet him. I was at a party and i actually met this guy. When i was there, he put his arms around her when he was next to her just to piss me off, he even whispered into her ear, "what do you think he would do if i kissed you right now?" i didnt hear it, but she told me thats what he said after the party. Since then, she has hung out with friends and when with them, he's "unexpectidly" come by. They've talked and all and she tells me that he apologizes for his rude behavior when i met them. But a few days ago she was with friends and he was there - she ended up doing coccaine (not the first time). she was open to telling me about it and asked if i was mad - i said i was only dissappointed but glad she told me. And she does tell me when she sees him - just so nothing is under the covers, and she asks me if i am okay with it ("I hope youre not annoyed"). But what kind of gets me is that she is going to this 3 day concert this weekend, and she is going to be camping with her friends - which are good friends of his - so they will be seeing each other throughout the concert. She texted me today saying that she is going to be with him for a little while because she wants him to buy her alcohol and so that she can plan the concert so that "there will be no drama." Even though we have been together for such a short time (3 1/2 months) we love each other. I care more about her than anything. I would die for her. And i do trust her. I understand that if there is no trust, then, there is nothing truly there. What i dont trust is her ex... trying to get her drunk or something... I honestly dont like anything about him and want her to stay away from him - but she insists to stay his friend. She tells me that its just something i am going to have to get over. When she asked me if i was annoyed i said of course not - but should i tell her to just back away from him and never talk to him? What am i supposed to think when she is away at this concert this weekend?? She says that there wont be any cell service, so i wont talk to her at all throughout the weekend. What do i do??????? Honest answers seriously. Her and i are in a serious relationship - our parents already bought us tickets to go outside of the country this summ