Search Results: going to the bathroom together

I really need to find out if my best friend or boyfriend is lying! Here's the story:

The other day in class, they were talking about a secret. He got really sad and went outside, they wouldn't tell me what was going on. I asked my best friend over text and she said straight away that he told her that he liked both of us (while still dating me). I got pretty upset because I asked him earlier in the day and he said no so he was lying. The next day I.....slapped him in the face (oopsss) because I was very disappointed that he didn't tell the truth. I then found out he doesn't like he and she made it all up, apparently doing it to all of his relationships. I got them to go talk about it during break and she came up and said that she made it up. The hard part is now she's saying that he doesn't want to tell me because it's 'personal' to him and he's making her lie to me. I got really sad and walked away with another close friend and 5 minutes later I saw them talking alone together again. She came up to me again crying saying she was sorry and we hugged for like 5 mins because I was crying as well. When we went to the bathroom to wash our faces she said again that he's making her lie but I'm confused on why she would listen to him. My boyfriend denied all of this but because I don't know who to believe I'm not on anybody's side. A mutual friend of my boyfriend and I told me that my friend likes him and wants us to break up and wants he to become his girlfriend again (they used to date). Very confusing but I need help. Who do you think is lying and how can I prove it?