There wouldn't have been a warning in the world that would have prepared Tony for a move like that and he let out a noise of surprise that might have also been a filthy expletive but he wasn't even sure what was coming out of his mouth anymore because he was too busy being impaled by Steve's cock.
The movement and then the position, the way Steve was rubbing up against his prostate nonstop, had Tony whiting out for a minute there and it was only Steve's hand around him, that firm grip that had him clawing back to a place where he could almost sort of maybe pay attention. "Steve," he said, because it was all he could say, and it came out on a moan.
There was no real moving forward to thrust into the grip and he was a little more into that than he might have otherwise guessed, but that didn't stop him clenching up a bit before he relaxed into it -- he could (did) trust Steve to give him exactly what he'd asked for and what he needed. He was right on the edge as it was. "I love you." It felt important to say even though he could have just as easily begged or given in to some far dirtier.