This was some years ago so I'm thinking it's a long shot but this was a post apocalypse world, there was zombies but I don't believe they were ever really called that. It was a group of survivors military style looking for a new place to settle and they find a good spot in an old Walmart type store and think there's no one around but turns out a survivor has cleverly been hiding there for a long time. They manage to capture him, for his own good. It was m/m but also had m/f. There was bits like a decomposing body in a bath tub and growing veggies in a massive bin.