Are there legitimately men who ONLY find their gf/wife attractive? Is it unrealistic to want that?

Yes, it is unrealistic. There are no men and no women like this. If this is your standard, you’ll be forever alone. Just because I find Brit Marling or some random woman in the grocery store attractive doesn’t mean I’m gonna leave my partner to pursue either of them. I’d be very, very worried about the person who didn’t find anyone but their partner attractive.

That speaks of obsession and probably poor mental health and I would be avoiding those people.