The once a year thing that you have quoted is absolutely out of order. He is saying that he will be content with you doing something he knows you dislike if you agree to do it only annually. Just how wrong is that. He should not be taking pleasure in you doing something he knows you do not like AT ALL.
Sexual relationships in normal couples are about sharing pleasure and enjoying making the other person happy.
I absolutely agree with those who say he has been watching porn - and also googling what he thinks you should like doing in order to coerce you into doing it!
It does not matter at all what the activity that you dislike is - everyone has their own red lines and tastes. It is very difficult when one partner starts to watch porn and a previously stable and happy sexual relationship gets out of kilter because of changed expectations on one side. There is of course no reason why a sexual relationship should not develop over time and change, but the bottom line is that neither partner should be doing something they do not want to do.
I know of what I speak. I had the same with my OH, and it damaged a previously happy and satisfying relationship. He started to try and get me to do things that I really did not want to do; to be fair he did not do things if I asked him not to; there was no physical coercion. But it left me feeling inadequate and unacceptable; and it made every sexual encounter a minor battle ground, instead of the happy moment that it had always been for many years. And this never changed until the day he died. And now that he is gone I have to come to terms with it all, constantly reminding myself that I was not at fault. When someone dies, you do labour over the things that you might have done better or feelings of guilt for things not said or done; but I know that his dissatisfaction with me as a sexual partner was created from the artificial world of porn, and that I was in no way at fault.
I stayed with him - he had so much that was positive for all of us, and my children loved him and had a stable upbringing - but the pain of the destruction wrought by the porn he watched endured throughout our marriage and has stayed with me even after his death.
I am so sorry that you are facing these challenges as I know how unhappy it can make you. You do need to be clear in your own mind that it is OK to make choices; that you are in no way inadequate or lacking in some way; that you are important in this world.
Only you can decide what to do next - but never lose faith in yourself and your rights as a human being. I wish you every good luck in sorting this out.
This is why I get slightly irritated by threads that say that porn is OK - it is not.