AN: I wrote this one the night after I saw Infinity War the first time. I posted it on my AO3 account a month ago, but figured I might as well post it here too.
The journey back to Earth takes weeks and there's nothing to do but slowly go mad. Everything that happened on Titan is like a nightmare he can't wake up from. All those years spent planning for worst case scenarios and when the day came he wasn't ready. At one point he thought they'd actually done it, because they were the good guys and they always won in the end. But not this time. This time he watched on as his worst fears came true, everyone around him dying, and then Peter. Sweet, innocent, scared Peter, clinging to him, begging Tony to save him. And God he'd wanted to, but there was nothing he could do. No amount of brains or tech could fix it. All he could do was hold on in horror, use those few precious seconds before Peter dissolved in his arms, to comfort the kid. And then he was gone. Like everyone else, just snuffed out of existence. It didn't seem possible. Someone so beautiful and precious and full of life, couldn't just cease to exist. It was too much to process, too much to try to wrap his head around. He felt himself detaching from reality, trying to escape the pain that would crush him if he let himself feel it.
But he wasn't that strong, he could feel it seeping in, seeking to make him acknowledge the fact that this wasn't some terrible nightmare, some twisted fabrication of his mind, but a devastating and unavoidable truth.
His throat felt tight, a nauseous feeling was settling in the pit of his stomach, and his vision was beginning to swim.
He wanted some diazepam, but he doubted Nebula kept any on hand.
It gets harder to breath as he realises this isn't going away. He's not going to wake up, Peter's not suddenly going to be here. He can barely breathe when it hits him he's never going to see the kid again.
His chest feels tight, his head is spinning, and his heart starts pounding. It's as though it wants out, like it knows he can't think about this loss as well as feel it, that that would be altogether too much to take.
At first it's silent tears, but before too long it's uncontrollable sobs, and then Nebula is there, the only other person left in the universe for all he knows.
"What's the matter?" she demands in her harsh, uncaring way. For a second he wishes he was more like her, that he didn't have to feel so much.
And how the hell does he begin to answer that? They lost, the universe is decimated, everyone is dead. Nothing turned out like it was supposed to.
He curls in on himself, rocks back and forward, lets the tears roll down his face untouched.
But there's one thing at the heart of this, one blow he can't handle.
"He's gone," he gasps. "He's gone, he's gone, he's gone..." And that's all that matters. That's the one thing he knows he'll never get past. It took forty-eight years, and countless battles in all arenas- with his father, in the boardroom, in the lab, in war zones, and with his inner demons- but Tony knows he's reached his limit. He is broken.
In the end it took failing a seventeen-year-old kid from Queens, one full of pop culture references, angelic purity and unshakable loyalty, to do that. And this time the damage is permanent. He's lost the person he needed the most, and without all the parts, without the most important part, there's nothing he can do to fix any of it.