Bestfriend hooked up with first love?

I found out my bestfriend since elm school, pretty much my sister, got drunk, went to a party and had sex with my first love. she called me crying bc she hardly remembers it and she said they put something in their drink and raped her. i found out that was a lie bc my other ex was there and he wouldnt lie about it. he said she got drunk with my ex and they had sex. at first she didnt tell me about having sex with him, i found out. i tried to just ignore it but i exploded one day. she said it was no big deal and that i said i hated him anyways. she knew i did love him , but i found out he was an aid infested dirtbag heroine addict. but she still did it and i want to forgive her. i want things to be the same between us. do you think its right?