That kiss was the chance Tony needed to realize how fast he was breathing and try to even it out before he made any more mistakes. This wasn't a good moment to get light headed from the terrible job his fleshy body did functioning without Extremis, how did anyone else get by? It was more difficult for Tony to smile, even in the warm glow of Steve's (easily one of the most reassuring and beautiful things Tony had seen), settling with his hands in his lap on a flirtatious smirk with his lip between his teeth and eyebrow raised expectantly. Now that he knew the plan, he didn't feel nearly as terrible. Even though he had just said that, like an idiot (but it was Steve, who he could trust and wouldn't use it against him and knew when Tony was using it against himself), and even though he could hear his dad so clearly, loud over Steve's joking, lamenting that he knew he had raised a goddamn sissy.
It was like Tony had to tell him. His smile was gone by the time Steve was holding out the ring (he got a ring? It was stunning, really, a tiny attack on Tony's heart in the grand scheme of this production, when he would have thought an engagement ring in this situation could only be tacky and misguided and he would have preferred none at all to some diamond, and then there was this ring) and waiting for Tony's actual answer, when he was supposed to talk instead of interrupting, but he reached up to squeeze Steve's shoulder and took the ring from him. He wanted so badly to just say it, spit it out, tell him yes, dammit, but instead he was sitting up to pull Steve into a hug and push his face against Steve's neck. "Wouldn't you?" he finally laughed and squeezed him tighter.