Based on the erotic game by Orcsoft.

I get the feeling that my wife has gotten more beautiful as of late. It's a small thorn that's stuck in my side and just won't go away. Niggling at my conscious that something may not be quite right.

After much deliberation, I hire a private detective to investigate my wife's activities and I regret having ever thought of doing so...
You see, having learned of your wife's adulterous affair with another man turned you on, made you burn bright with lust... like a horny beast.
You wish you never learnt this feeling but... at the same time you wonder how you could have ever been satisfied without it...

NTR... A forbidden delicacy. The dark swirling lust within you beckons... to draw you into a deep abyss, a never ending fall into cuckold depravity.
Enjoy... as your wife moans and groans in the throes of pleasure...
... with another man.

(Source: DLsite English)