What a complicated and difficult situation! And what a complicated and difficult man you once loved and married. On the one hand, he is a “compulsive liar and cheater” who has hurt you and left his sons without an involved father. On the other hand, he is scrupulous about paying his child support, he supports his young “wife” and her extended family, and he left you with two wonderful sons. No wonder it’s confusing to figure out what to do.
I think you’ve been extraordinarily wise to refrain from telling your sons all about their dad’s failings. I encourage you to continue as you’ve done. Let the boys come to their own conclusions. As adolescents, they may think their dad is the fun parent. But as they grow older and mature, they will come to understand that you took the “high road” and let them have their positive view of their father while they were growing up, even though he hurt you deeply. They know that you love them and have never left them. They will eventually appreciate the discipline and the support you have given them. I think you can trust the good values you have given your boys. You don’t need to say a thing about their dad. As they learn more, his behavior will speak for itself.
I wish you well.