Well, I think because you wanted it to be amicable, even if it wasn't. Fact is, you divorced out of self respect, not because you were out of love with him. His infidelity forced your hand, and it's not the easiest thing to just get over.
I think if there is some sort of group therapy of some sort, and even if it's on a different issue, I'm thinking that these ladies who divorced their abusive husbands who have a group may be a good place for you. Some of them still love their husbands even if they were beaters. They would understand where you're coming from.
Don't think you're weak, because the fact that you still loved him while you divorced meant that you were strong enough to do it for yourself, and that's not an easy feat to accomplish. The fact that you still have the ability to love (especially him) means that you have great inner strength. Please utilize that inner strength to take the next step.
You can do it, I have faith in you. You've shown in the short time I've known you that you are a strong spirit.