Maybe if Ianto had warned him, if Sulu'd had an idea of what he was planning, he could've held on longer, could've planned for it himself. But when Ianto brushed against that place, Sulu moaned and ground his hips against Ianto as he came, his stomach twisting pleasantly, muscles tightening and all his thoughts flying out his head. He knew his nails were digging into Ianto's shoulders, and that he was making a few (possibly unsightly) noises into Ianto's ear, but he couldn't help himself.