Husband cheated and gave me herpes

So this is going to be a long story.. My husband and I went to Arizona because he had a contract job for 9 weeks. We were fighting a lot because we were stuck in a hotel room and we had our 11 month old daughter with us so it was chaos. So for some reason I started feeling like he was doing something behind me back. He was going in earlier and getting out later. He was working from 10:45 pm to 8/9/10 am. At first he was coming back to the hotel around 8:30/9. A few weeks in he started coming back around 10. I thought it was just because of work. Of course I don't want to think he's doing something I mean we're in a town that we've never been to before so who could he be with? Well one day I saw cum on his shirt and pants. Whenever we have sex with clothes on I leave my cum on those exact same spots were I saw the cum. Well I thought he was just jerking off but now it makes sense. Also he "lost" his wedding ring and he found it in the work truck he drove. He started noticing bumps around his pubic hair and said he cut himself with a rusty razor. So I thought it was an infection from that. Well it went away for a few days and when we went back to our hometown the bumps came back and I started to get bumps. I went to the er and its herpes... I didn't know what to think. The doctor said he could've had it for years and never had an outbreak and when he cut himself it triggered it. So I gave him the benefit of the doubt and we were moving on. Well I get a message this morning on FB and it's a girl telling me her friend told her that her friend is spying on me on fb and looking at my profile. She doesn't know the girl but apparently she's the one that my husband had an affair with. She said that they were hanging out and having sex when he was in AZ. My heart broke... I couldn't believe it. My husband? No no no... he wouldn't do that to me... I always told him my biggest fear is him cheating on me.. I thought what if this girl is lying? What if it's her that had the affair and she wants to break us up? Well everything makes sense now. He would go in early and come home late. He had cum on his clothes. He "lost" his wedding ring. He gave me herpes from her... while I was getting all this info he was at work. So I asked him to please tell me the truth because someone already told me everything. He said some girl hit on him at the gas station and he gave her his number but that was all... I want to believe him I do but i know I'll be lying to myself. I have to let him go and file for divorce. What do you ladies think... I'm so hurt I never thought he would do this to me...