Should I tell his bride what we did last night?

Too bad just got this Mail now..hope it's not late.Her case is on another level and I trust you all to give her the perfect advice...
 Emeh today is my bestfriend' wedding but last night I went to her fiancee's house to collect something for her. One thing led to another and he told me he had always fancied me and wished he met me first.We had sex twice.This morning, I told him if he loved me he should tell her how he fancies me and he said I'm a whore and a prostitute. I'm a decent girl and this idoit feels he can just use me.I feel so bad and I want to tell my friend what we did because she is marrying an asshole and a fool
 She feels he is perfect.Please help me ask your readers what I should do.I'm tempted to tell her today ‎