Do you have an obligation to talk to your parents?

I would say no you do not have an obligation to talk to him if you don't want. But don't hold a grudge against him about getting with his "mistress". Your mother and his relationship was probably over and he went about it really wrong but he had to do what he though was best in his life. My father did the same thing. But we still have a relationship somewhat. I don't have any hard feelings and don't care that he left my mother but it is not like we talk on a daily basis either. We talk probably once every 2 months.