My friends promiscuity is ruining my reputation..what do I do?

Ok first, if your boyfriend does not trust you then that is not the man for you. But if her lifestyle bothers you then you need to stop hanging out with her. You also have the option to hang out with her only in situations where things can not happen. Invite her to your house for movies but not to the club. If she a good enough friend you can talk to her about it. But you must be nice about it, do not point fingers.