Han wants to stay away from the whole situation but in reality he can't no matter how much he tries to. He cares too much about Luke and Leia and doesn't want Anakin/Vader to hurt them. Also he's so hostile towards Anakin because he had looked up to him so much that knowing he turned out to be Darth Vader, the man who not only tortured him and put him in carbonite but he also tortured Leia, destroyed her planet and at the same time caused Luke so much suffering. It will be hard for Han to forgive him but eventually he will.