Immediately, Bruce put a hand on Tony's shoulder. "Tony, stop." He said gently. "You're not there, it isn't happening, you're just imagining it." Tony's coughing lessened slightly but didn't stop.
Surprisingly, Steve was the one to think of something to say to calm Tony down. "It's not real, Tony. Nothing you're seeing is real." He said softly.
Tony froze, and Natasha could hear Bruce's sharp intake of breath and see the flash of fury in his eyes. "Steve." She warned. "Don't say anything else."
Steve looked apologetic. "I'm really sorry, Tony."
Tony looked up, his gaze so full of pure hate that Steve shrank back a little in his seat. Then Tony ducked his head, his body wracking in silent sobs. It was shocking how quickly that his mood changed. "Don't say anything." Bruce said slowly. He then turned to Clint, who was flying the quinjet. "Can you slow the jet down a little so I can get out of my seat?"
Clint opened his mouth to speak, but remembered what Bruce had said and simply nodded, slowing the quinjet. Bruce unclipped his seatbelt, lowly getting out of his seat. He knelt in front of Tony and took Tony's hand in one of his own. "Tony, it's okay." He whispered, gently rubbing his thumb over the back of Tony's hand. "Steve didn't mean that. He doesn't know what it means."
Bruce unclipped Tony from his seat and lead Tony over to a bench, which was usually used when people were kitting up to, say, jump out of the quinjet. Both him and Tony sat down and Bruce pulled Tony to his chest.
Natasha could see that Bruce was having trouble holding it together, and he had a good reason to be finding it hard. She'd seen Tony's face briefly as they'd sat down, and Tony had gone ghostly pale and there were faint tear tracks on his face.
They sat there for a long time, no one doing anything but breathing and in Clint's case, flying the jet. Bruce and Tony were still holding each other tightly, and Natasha was pretty sure that Bruce was crying, too. His breath intake seemed to imply that, but neither of them were making a sound.
Steve looked awkward. And very guilty.
It took a while, now that they were going slowly, but Stark Tower finally came into view. It would be a few more minutes to get there, but no one minded, compared to the near-hour they had spent in the jet so far. Thor hadn't slowed with them, so he had long since landed at Stark Tower and would have spoken to Pepper.
Tony and Bruce were still sat in the same position, but now it looked to be less of a comforting moment and more of an intimate one.
"Terribly sorry to interrupt," Clint said, a hint of glee in his voice, "but we're landing now, so you need to get back in your seats."
"You sound like a flight attendant." Tony said, grinning. All of his usual snark was back. "'Please return to your seats, we will be encountering unexpected turbulence.'" He said, mimicking the voice of a flight attendant. Clint laughed good-naturedly and started to land once Tony and Bruce were back in their seats.