Is It Wrong To Think About Other People During Sex?

Almost every time we have sex, I fantasize about someone else. I’m usually thinking about someone I know that I’m attracted to, someone I’ve had sex with before, or porn that I’ve watched. I also fantasize about people other than my partner when I masturbate. To be honest, I’ve never felt guilty about it but sometimes, in the moment, I’ll think, what is wrong with me? I know that if my partner knew I was thinking about someone else when we were intimate, she’d be devastated.