Cheating

So my bestfriend set me up with this boy that lives about 3 hours away from me. I asked my friend if she was fine with me and him and she didn't care that we were close. me and the boy met up yesterday. We planned to have Sex and we did. But she she suddenly has blocked me and I didn't know why I just thought she was jealous of us. I found out from a friend of a friend that my bestfriend had had sex with him also the night before. I asked him about it and he said it did happen and it won't again and he wants to be with me and I don't know what to do.