Girlfriend advice... Please help :(?

Okay I really need help on this one. I'm a 16yo male, dating a 15yo female. Were both in high school, but different ones. I love her so much, and I know she loves me too, but she screwed/s up a lot with our relationship. In October or november of 2010, she kept talking to this guy who used to be my best friend and who goes to her school. One day they were standing outside her locker and he kissed her, and she kissed him back. She never told me this until January of THIS year, after I finally got it out of her. It wasn't just like a peck, it was a full on makeout. Now she did feel really Bad about it, and cried a lot about it, but now it's April and he still texts her. That's my first question- if he's still texting her, and she tells me she's not texting him back, do you think he would be that diligent for 3 months or is she lying to me? Also some more background info, she went to a church camp over the summer and she met a guy there, I know for sure nothing happened but he tells her that he thinks of her when he has with his gf... Idk what to do about that :/ and they still text as well. Also she's a bit of an attention , she talks to a lot of guys besides me and hugs them and stuff, I know it's not a really serious thing but still it really bugs me. FYI ive talked this over with her before, but she doesn't know it bugs me this much. Sorry for the long story, but what should I do? Input from both guys and girls is accepted, please be as critical as you want. I still love her and want this to work.