Stupid question haha..

Fiancé claims he only gets hard for me ( sexually ect ) and he says he doesn’t even get them at work not even if a girl with her tits almost hanging out ( he works in grocery) he simply ingores them I used to work in clothing there ect

But can a man only get hard for their S/O if they don’t find another person attractive?

I get it erections are normal but I’m talking about sexual ones ect