Or 10? Or 20? Is it even possible?

I've been with my girlfriend for about 5 years now, living together for the past 2. Even though my overall sex drive hasn't decreased, my desire to have sex with her has basically fallen off a cliff. It's gotten to the point where we only bang a few times a week, and most of the time I'm mainly doing it out of a sense of guilt or obligation. This is despite the fact that she's a solid 8/10 and will do literally anything I tell her in bed. I honestly have no idea what we could change that would help. She hasn't gained weight or gotten out of shape, the physical attraction just... isn't there anymore.

What makes it even more confusing is the fact that I could easily bang the shit out of a 5/10 that I'd be too embarrassed to tell anyone about, but my girlfriend could be gargling my balls in her hottest lingerie and my dick wouldn't even flinch.