18+ Isekai Furin: Maou Toubatsu kara 10-nen, Tsuma to wa Less no Motoyuusha to, Otto wo Nakushita Onna Senshi

Getting hit by a truck and sent to another world to face off against the Demon King 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?

(Source: Seven Seas Entertainment)