Resentment and Betrayal

So just recently I found out that I was cheated on by the one person who was supposed to be my best friend. I want to forgive him and honestly it didn't shock me as I though it would but I resent him for it so much. I'm thinking of going to see psychologist again because of this. I just can't seem to get the images of them out of my head. I want them to go away so bad but I can't make them. I want to work it out with him and I know that it can be done. And no I am not and idiot for taking him back after this happened. The images of them come at me like a ton a bricks and it feels like I can't breathe. Luckily it's not all the time, it's only come occasionally. I don't want to think about them and what they did. I don't want to picture them having sex and kissing. For some reason the fact that he kissed her hurts more than the sex part of it. I don't really know why. I'm glad I put up walls weeks ago when I first started expecting him of cheating on me. I mean it's not like I'm completely stupid. When your relationship goes from here babe answer my phone to just let me delete this right quick, and he comes home with scratches all over his back and says it's just from wrestling I know somethings being kept from me. He told me and said he'd been wanting to tell me for a while. He said he felt horrible about it. I'm not really sure what to believe on that area though. After he tells me he did is several times with her in one day, I just don't really know if I can believe that he felt that bad about it. I feel better now that it's in the open. These past couple of days, we haven't argued at all about anything really, but it still hurts. I feel like we can work through these issues and come out stronger and raise our child together but I just don't know how long it's going to take to get over this. The internet keeps saying it'll take me two years to get over it and we haven't even been together for a year yet. I just needed to get this off my chest. I just really wish someone could tell me what to do.