What are they thinking?

sorry this might be abit long, but people please give me some advice. Right. the other month I had sex with this lad, but we didnt really tell many people cus well its no1 bussiness, but my best mate found out, but nothing was ever said. but last night I was with this lad, we didnt do nothing just talking as friends ya know. but somehow my best mate knew I was with him, and she txt me sayin your shaggin him. even tho I wasnt. and well now shes bein funny with me and I have no idea why cus I have not done nothing. and even if I did it had nothin to do with her, and I just have this feeling that she is gunna tell people that I’ve been havin sex with him & its really peed me off because it hurt him as well, and im getting acused of doing things I havent and she is ment to be my best friend. what can I do ? :(