My wife secretly wants to be a fuckdoll

I know she wants it. I see it in her eyes, in her jokes and in her nerves laughs when she realizes that it may be obvious. I feel it when she tries to suck my fingers while i fuck her, or while she deep-throats my dick and feels my hand crawling up her legs to her big fat ass, then slide down between her butt-cheeks and move right in that wet smooth, pussy. Exactly at this moment when she slightly moans but as if screaming inside, arches her back even deeper, rocking back and forth on my fingers, I understand, that she is begging me to make her fantasy a reality. She wants another cock in her while she serves me. I can almost hear her say "papi please, I need it" like d**g addict but in her case its need of thick stranger cock.
Dilemma is that she is scared to admit it to me and I'm afraid to tell her that I want to see her riding a stranger while I see her mouthful face and rolling eyes. What should I do? How should I do?