I think we as adult women need to learn how to take responsibility to see that our feelings are validated, and if they are not, take responsibility to leave.
If you do not see movement in your boyfriend's wanting to take responsibility to factor in your own feelings and welfare within the family, it is you who has to change this.
I am struggling with the same thing, and so is the man I have been with the past 8 years. In my case, the adult child is my own.
I feel for you. I agree with you, the behaviors you are talking about with the son are beyond troublesome. But the Dad is not hearing you. What can you do, except protect yourself? Perhaps if you back off, Dad alone will take the steps he must, for his own welfare and that of his adult child.
Welcome. I hope you keep posting. It helps.