I am going attempt to make an analogy here. You Dad is living his life as he must. For whatever reasons, things have broken down between your parents, their marriage seems to be over, and your Dad is seeking normal companionship as he is not a Monk. He is reluctant to discuss what he is doing with you for the very same reasons that a gay person is afraid to come out of the closet to his family. He hasn't sorted out his own feelings yet, he feels some shame and he fears a bad reaction from members of his family. He would probably like to get this out in the open, but isn't able to do it yet. And you are like the relative that discovers that a family member is gay and cries "It's all about me! It's all about me! He has been sneaking around being gay and I am disapointed in him and I am only worried about how I am affected by this and how this reflects on our family dynamics! How dare he?" And you embody the reason that he is afraid to approach the subject by the attitude that you are displaying now. Just some food for thought.