Man Who Fell for a Knightess Whore Has His Cuckoldry Fetish Deepen Ver.1.01 by Suzuya - Adult Sex Game

Within the defeated kingdom of Grubenhive, our main protagonist became a prisoner to the antagonistic Raymond Kingdom.
Forced to engage in grueling labor, he was saved by a group of knights fighting to liberate their homeland.

He was infatuated with Sera, the leader of those knights, but soon became of the crushing reality that she offered her body to boost the morale of her colleagues, and to raise war funds from the wealthy.

He had neither the wealth nor the strength to help her, and vowed not to see her as an object for sex.
Despite his diligence to help her fight, he began having emotions more complex than pain and suffering whenever he thought of Sera having sex with other men.

Eventually the war ends, and both of them become husband and wife.
And in the midst of their happy life, he realizes a deep-seated fetish he had hidden inside of him...