Horrible jealousy, how to deal with it?

I was talking to a female friend of mine, same as as me (18) and I really, really like her, but sadly she already has a boyfriend and she's not interested in me like that. Last night we were talking and I asked her about her evening and she said she'd spent it with her boyfriend (of 2-3 months), and in the middle of telling me what they did she said "and um lots of other fun stuff," and of course I know what that means. Basically, I just get extremely jealous that she is with, and has sex with, someone else, and I know I have no right to control her, and I don't want to. I only feel this way because of how strongly I feel and care about her. It also doesn't help that I'm a virgin who's only kissed a girl and she's had sex with two guys now. How do I deal with this?