It's further than he ever thought he'd go with Ianto - pretty much as far as he would go with anyone from this side of the equation, even though he's happily taken far more to his own body - and it feels amazing. Watching Ianto, feeling him shake, hearing him scream, and then feeling him clamp down, vice-like, around his cock as he comes. He doesn't care that Ianto has no words because every sound Ianto makes is screaming his name, and it pulls him apart like nothing else. He comes too with a roar, shuddering and shaking, fingernails of his one hand digging Ianto's hip as he clings on for dear life.