Sex rumors

I don't know what to do....  There are rumors going around my school saying I've slept with over 20 people. I'm not a virgin but my number is no where near 20... My friend and I like each other a lot and where about to date, his friends keeping making fun of him for liking me and telling him horrible things that aren't true. His family is disappointed in him for liking me, but I don't even know them.... After his family said they where disappointed in him he stopped wanting a relationship. These rumors are ruining my friendships and relationships. He said he believes me but I don't know what to do about any of this. Any advice?