It’s his problem, not yours. You’re under no obligation to do a sex act with which you’re not comfortable.
He absolutely should respect your wishes full stop end of discussion. Having tried something one time or a million times regardless of what it is does not mean you’re obligated to then do so again for the benefit of another. His childish temper tantrum is manipulative and aimed at getting his way. At the end of the day if it’s nothing something you want to do, not something you enjoy then he needs to grow up and respect your wishes.
Wow he is being a manipulative baby. You said no, and that’s it.