I still want to find out what exactly happened

Let me just say, my story about my relationship still remains a mystery…however I do still want to find out what exactly happened. My partner cheated on me, we are at the stage where it still hurts. It happened in March 2021 however, from the pieces I do hear about when I do drag it out of him he gives me information on the situation. It’s like he doesn’t want me to know happened to between him and the girl fully. It’s weird. They knew each other from a gaming app. We all knew of each other, she was aware he had a partner but for some reason she was interested in him and I kept warning him about her. It was like he didn’t believe me. Months flew by and I was sleeping with my enemy reallly it feels…he was giving her the attention she should’ve been giving me. We were going through tough times during the beginning of the pandemic but i did all i could to make sure we were both good and did some what. But it hurt finding out he had intentions of fucking her, i saw their plans and it literally made me sick for weeks. Crazy thing I had a dream a week before about him cheating. Now that the damaged has happened to me I have been trying to accept what happened but how can I when I don’t know what really happened to between them. He said it was just sex but i feel it wasn’t. She let him knew back in December 2021 she liked him, three months later i found out him and and her are keeping in contact through discord. It’s months later and I With him but things haven’t been the same. I cant trust him like I use to. I want to move on with him but this just won’t shake me.