My Dad Has Just Married. What Should I Do As The First Son?

It is very difficult to say because i don't know what you are going through and what exactly is your relation with your father. I would still suggest you to be patient and try to love and respect him in the same way.

Your question is not very clear as to what you are asking,but from what I've concluded you are your father's  son and you will always be that nothing and no one can change that. If you have a relationship with him don't change that conversate with him, do things with and for him don't change. All that is required of you is to respect his wife nothing more or nothing less Peace and the best of luck.