ISEKAI AFFAIR: 10 Years After Defeating the Demon King, the Hero Cheats on His Wife With a Warrior Woman Who Lost Her Husband Vol. 1

Getting hit by a truck and sent to another world to face off against the Demon Lord was the best thing that ever happened to Yuuta. He attained unmatched powers, saved the world, and even married the princess. But now that the adventure's over, he finds himself in a boring, sexless marriage with no battles left to fight. The only excitement he can find comes from sneaking out for intimate nights with his former party member. Can the powers he once used to save the realm keep him from getting busted by his royal family?