So this guy is actually one of my best friends/guys I like. And we've talked about how we liked each other, and we hookup a lot but lately he's been hanging out with this girl I don't really get along with, and I'm afraid he'll start liking her. He's tried having sex with me but I told him wasn't ready and he said that was fine. But I'm afraid now if I don't have sex with him he'll leave me for hannah considering she knows what she's doing(she had sex multiple times) I'm just scared to lose him, I think I really like him. By the way I'm 15...

NO NO NO. never have sex just to please or make a guy like you or for whatever reason it is. Chances are he'll leave you rite after he gets what he wants. If he really like you he won't go with some other girl if he does e was never worth it. Trust me If he leaves you just for that he doesn't deserve you

To have sex with a guy just to keep him away from someone else is about the dumbest thing you can do. Sex is not a bargaining chip. It is not something you use to keep someone. That is a bad habit to start.
The guy either likes you or he doesn't.
At 15 your are not prepared to be a mom. This is not the situation in which you want to lose your virginity.