My husband constantly cheats

My husband and I have been married for 9 years. Out of those 9 years he has cheated on me during 8 of them. He has cheated while I was pregnant with both my children and even left me when I was pregnant with the first one and attempted to sleep with a prostitute when I was pregnant with the second one. I have taken him back over and over, many times without any explanation or apology from him. A year ago I found out he had cheated with a lady he worked with. I forgot to mention he is a truck driver and is gone all the time. He met this lady at the driver school and they began to have an affair. When I found out about the affair it had been going on for 5 months.
I had some suspicious before I found out but he always denied it. He always says he doesn't know why he did it when I confront him about it. After I ask him several more times he always find a way to blame me by sating he couldn't talk to me, our sex life is not spontaneous or that he has lost the desire to be intimate. After this last affair I told him I wanted a divorced he broke down emotionally and begged me to give him another chance.
Since I had never seen that side of him and he started to open up more and apologized repeatedly I decided to give it a try. He promises me that he would stay away from the porn and that he would never cheat again. I accepted his promises but not without caution and suspicion, I mean I had heard that before. I thought we were working things out good. We were communicating better, we started praying together nightly, and we always told each other we love him/her before getting off the phone.