[ Steve can be like a dog with a bone, but he's tired too, and less capable of hiding it (though not for lack of trying). Tony standing down and relaxing his posture takes the steam out of Steve's response. That, and he's ashamed that it took Tony letting his guard down for Steve to remember that they're both recovering. He should've insisted that Tony sit down sooner.

He doesn't have time to dwell on that, however, because then Tony is telling him that he's a good person. Sure, it's not "knight in shining armor," but it's something. Of course, Tony doesn't know that Steve's actions weren't purely selfless. Tony can't know, because this is progress of some sort and the last thing Steve wants is to end up back at square one.

It's going to be difficult to toe the line between saying what he wants to say and showing all his cards, but Tony could put that wall back up at any moment, so there's no time to waste. ]

Then let me be the first. You're a good person, Tony. I would've said that sooner but I— [ Steve realizes that this admission is much more honest than he intended, and that feels inherently uncomfortable, but he can't think of anything to else to say, so he adopts a different tone, trying to shrug it off, minimize it. ] —I didn't think you needed to hear my opinion.