Moving past cheating

My bf of 5 years went to go help his dad with something a week or so ago. After he was done with that he went to hangout with a friend and the friend girlfriend. They were gonna smoke some weed and he was gonna sober up and come home. Well I guess when he got there it was just the girlfriend. He stupidly stayed and smoked anyway. He says he can’t remember what happened. He said it was like he fell asleep. I’ve been that high before, so I know it’s possible. He said he remembers coming back to for a second while pulling up his pants. He then blacked out again and when he came to again he was in the car and driving, already half way home. He has never cheated on me or any of his exes before. We’ve had our issues, but never with anything cheating. He immediately came home and told me. He called her on speaker in front of me and she admitted that they had sex. He started the process of going after her for rape, but that’s not going to go anywhere. The cops are already blaming him for the situation and taking him out of pressing charges. So we will probably just drop it and try to move on.

I’m 20 weeks with my first. I am really struggling to move past this. I really want to move past it. I love my bf so much. And I want to work it out for our son. But I keep picturing him with her. I’m grossed out that he was inside someone else. I’m terrified he could have gotten her pregnant too. What if she had an std. he’s being tested and monitored for those by his doctor. He’s been so apologetic. I do believe that he can’t remember anything. The girl said that he was the one pushing for it. That I had cheated on him and he wanted to get back at me. That’s not true at all, I’ve never cheated. She said that said he handle touched or smelled pussy in months and wanted to finger her and wanted it so bad. He and I regularly had sex and I gave him oral and handjobs when I was too nauseous. We’ve always had a very active sex life. I know she had a thing for him and wanted to be with him, so I think she’s lying. He’s never been the type to beg for sex, he barely even initiates with me. I just honestly don’t know how to move past this.