You shouldn't feel like you need to be comfortable with sexual things that make you uncomfortable. With that said, I do have an analogy that might help you understand it more from his side:

Let's say a few nights a week you and your partner make a delicious meal together. It's the best food either of you have ever eaten, and you both put a lot of effort into it. By the time you're done, you're both completely exhausted and feel like you don't need to eat for days.

Before you met your partner, you regularly ate fast food. You rarely eat fast food now, but sometimes your partner does because he gets hungry on days where you don't cook together. You never really liked fast food, you just ate it because you were hungry and it was convenient. He, on the other hand, actually likes fast food and enjoys eating it. He has particular burgers that he likes more than other burgers, even though they don't compare to the juicy steak he eats at home with you. Eating fast food instead of cooking with you can end up being a major problem, but as long as the two of you make your cooking sessions your main priority it doesn't have to.

Anyway I'll avoid going into more detail, but my point is not everything involved with getting off has to be in competition with fucking. It's possible to like something that gets you off more than alternatives and also be in a committed relationship with a person who you have super satisfying sex with. It's up to the two of you to set boundaries of what kinds of things that get each other off you are comfortable with.