I guess it depends on your reasons for not wanting to do it. I always believe that each person has the right to set their own sexual boundaries, and that those should be respected by their partner(s)… but there’s a difference between something you absolutely cannot do, and something you choose not to do because you find it slightly off-putting.
If it’s a fear you have because you haven’t done it much in the past, it’d probably be good to face that fear and get over it. No use holding onto anxieties, especially in areas like sex which are supposed to be joyful.
But if you’ve tried it enough to know that you just don’t like it at all… then I think it’s reasonable for you to maintain that boundary. We all have things that we just don’t do, and that’s fine as long as you’re with someone who respects that limit.