How do I forgive and forget when I hold so much resentment?

I have been with my husband for almost 10yrs. We have 3 gorgeous daughters and a stable life. He use to drink a lot and actually just recently stopped. He couldn't tell me where he had been or what he had done the night before. I know, this was tremendously scary. When we first met, I was saving myself for that special one. I had never been with a man, or even kissed. He however had been around the world many times over. I feel in love with his looks and also just the thought of having someone care about me besides my family. He cheated on me the first time when he worked as a gas attendant. I found over 20 numbers with descriptions of girls. I don't know if anything ever went down as I never caught him. A few years later, he bought his own car and was taking himself to and from work, to the gym, etc. He would come home drunk sometimes. He would always say he was at the gym or something. I later found a cell phone in the glove box of his car that he had hidden. I listened to the voicemails. Once from his sons mom saying she was at his job and where is she suppose to meet him(he later told me he met up with her to give her money for his son-I believe this to be true) the other message was from a girl asking him when they were going christmas shopping. There was a couple from her. I confronted him in sever anger he told me she said she felt bad for doing this. He has never went any further then that, he said they were old friends, she is horrible ugly, and they only drank and played bball. I can't believe any of it. I hold such horrible resentment. How could he do this to me while I was at home caring for his children. He said he did it because we weren't getting along. I told him that was an excuse. I just don't know what to do. This was over 2 yrs ago and I still feel the anger that I felt that same day I found out. Can someone that has been in my shoes, that maybe has a Christian stand point, address this question for me. How does one forgive? I know I will never forget, trust me I know that. But forgiving something that in my mind is so horrible., I just don't know if I can. We go out and he might pay the female cashier, and where before I could care less, now I get so angry at him for nothing. Just because I think in my mind about what he did in the past. I know it is not fair to bring it up to him all the time, but he has never really spoken about it except to say "I don't know" this makes me so mad I don't know what to do with my emotions except scream! He just wont talk about it and I just want to know the truth so my mind doesn't go on and make up a false truth.