AITAH for not “doing the deed” with my partner during their period?

It’s pretty straight forward: I get queasy with all things blood. My partner doesn’t seem to care how much it affects me and keeps asking me to do it. I’m having trouble communicating to my partner how uncomfortable I get, but I also don’t want to be selfish. I want to put my partner’s needs ahead of my own, but I just don’t know.

Any idea?