I agree that it's absolutely up to the owner of the penis. I also have a lot of sympathy for the OP's fiance.
OTOH, I've never been with an intact man, so I can't speak from personal experience. But, I know one woman who says she's never had non-painful sex with any man who was circ'd, and never had painful sex with am an who was intact. This is obviously not the norm (I've certainly had lots of non-painful sex, with only circ'd partners), but it's very difficult for the OP to talk about what this "will" mean for the two of them, as she can't know what it will mean until and unless the circ is actually done.