As an Instructor I cringe every time I hear someone say that they want to learn to dive because their significant other wants them to.
I cringe, too. Whenever I suspect it, I find a way to pull the person aside and let them know it's up to them and that I will support them either way. If they don't want to dive, I don't want them in the water. Once they feel like it's their decision to make, things change, and virtually all discover that the at least want to try diving.
If you're truly don't want to learn to dive, tell the instructor.