School rumors?! What do I do?!):?

There is this stupid rumor going around school that I have my boyfriend a blow jobb and it's completely 100% FALSE!): but what makes me sad is that I found it out through my boyfriend because he told me that some girl had asked him if I had done that to him! And I told my best friend about it and she said that she had heard that going around too! So I asked her if she could please tell me who it was that started it (because she knows who did) so I could get this whole thing cleared up cause the rumor makes me look easy and stuff but she doesn't want to tell me!! And now more people are talking and I don't know how to solve this I mean I don't want to get angry and cry and get upset about it when I know it's not true but I don't want to defend myself either cause it makes it seem like it is true plus knowing that people are spreading and believing this stupid lie only shows me that those people aren't my real friends but since I don't know who's spreading and believing it I don't know who my real friends are! And this is really nerve wracking, upsetting and humiliating)): what should I do?! PLEASE PLEASE PLEASE HELP!!):