Who's lying?

Okay ladies...

So my fiance has a little history of talking to females. It's only happened once when I moved out. He never proceeded to hang out with them or anything. He just talked to then. Which I know for a fact since then he hasn't talked to any other female. I am currently living back with him and his family again.. Well a few weeks or so ago this girl came over to see his cousin who was living with them. And I went to bed early that night because I was very nauseated and tired. Well he stayed up and his sister who is my age woke me up and said that I needed to go to the living room because they were practically sitting on top of each other. So I did and what do you know she was right. Well. I of course assessed the situation. Speed up to this past weekend. First his sister tells me that the last time the girl was over him and the girl walked to her ex boy friends an apartment building a way to retrieve her clothes... But they were already here ??? So I confront him and he tells me that he didn't know and they ended up meeting them hers at the basketball court about 200 or so feet away from the apartment. Which I thought was suspicious because he would have normally woke me up to tell me. So anyways his little brother who is about 16 going to be 17 tells his mom who is like my best friend that my fiance was oddly taking showers in the middle of the night while this girl was staying the night with us. Which I know didn't sound right because not too long before we had taken a shower together. And he had the same clothes on the next morning .. Which I had a thought as to maybe it was so I didn't know he took the showers... Well then I confront him and of course I'm acting crazy!!! So I talk to his mom and she tells me to message the girl. So I do. I told her that he already told me everything that happened. She denied everything at first. So then I tell her she better tell me because I'll beat her up. She still denied it. So then I say look you tell me it's a free card no one finds out just tell me cause at this point either way I'm beating you up... So then she says there was one thing and starts apologizing A lot.. And says that is why she left the apartment so early. She said they just had a meaningless kiss in the shed. Then I tell her we'll there is 4 people who told me there is more that went on sexually so what was it did he finger you ? Did you blow him? Or did y'all fuck. Then she says it was the first two. So I confront him and he says I can't believe you're believing someone you met twice over your fiance... And he denied it on the phone with her. She says it did happen still.. But she never called him a liar and she flirted with him right in front of me a few times and I let it Fly... So was she trying to get us to breakup by lying or did it really happen? I really need opinions 😭😭😭😭😭😭