This is actually how the Seth/Zach fic Skin started, but it didn't feel right so I switched perspectives.
"She's moved on. Stop torturing yourself and let her go," he whispers, his tongue dragging along your neck, his teeth sinking into your shoulder when you turn your head to the side, granting him access.
"Not torturing," you mumble, your hands fumbling with the zipper on his pants. He's wearing khakis. They seem so practical. As far as pants go, khakis have to be the most sensible pants on earth. They are pants made for water polo players that basked in all their tan, muscular glory. They are bland, boring pants. Not unlike Zach himself. But underneath, past his belt and navy blue boxer shorts, there is something far more interesting. "Just biding my time until I pack on that extra forty pounds of muscle and can finally kick your ass." Hand inside his boxer shorts, fingers wrapped around his erection, you squeeze and his head snaps back. Now, you're torturing.