I am going to say this and I don't intend to be judgmental and if it comes across that way, I sincerely apologize. You said that you have anxiety and I can understand because I get test anxiety so I get that it just doesn't go away. You may not agree with your boyfriends dad, but if you see a future with him you need to start respecting him. If you get married and he will be your Father In Law and I firmly believe that the commandment stands with him as well. Also, if you have children do you want them to respect their grandparents? Children tend to repeat what they see their parents do.
True Story: My sister and her father in law do not get along and to be honest it is no secret. She has been known to yell at him and call him names to his face. My sister and I both were not raised this way and we know better than to treat anyone like this. But as a result of her being disrespectful to her Father In Law it has caused a major problem between her husband and his dad.
Again, I do apologize if this came across as judgmental and I am by no means saying that he is right and you are wrong, but what I am saying is no matter what he tells you, he still deserves respect.