I agree with Suki.
I was cheated on too. It hurts. The pain lasts a while. The only way that I dealt with the pain was to live it, walk through it and eventually it lessens.
Some people are programed differently. Cheating is part of their make up or at least they bend enough boundaries to where they are able to justify pretty much anything they want.
If you are at an odds with his behavior, then maybe you look into what you want in your life. You have the power and ability to have the life you want with or without this man.