Okay, this idea is too close to something that I'd done before in Book 5 of ITYWD, so I used that characterization and an excerpt from that.  Angst.

Pain.

So much pain...and so cold. Body shaking, mind numbing cold.

Everywhere.

Tony was afraid to open his eyes; afraid of the fate he was left to, but if he was to survive whatever hell this was, he had to. The last thing he remembered was running...no, crawling from the bullets and debris flying from every direction, barely seeking shelter behind a boulder before seeing his own blood and passing out. He remembered those soldiers...those kids who he had barely met, and he could almost see their faces still if he could bring himself to concentrate on anything other than this pain radiating from his chest. His breaths had become quick and rasping, his chest barely rising and falling with each one. He tried to regain some semblance of control, feeling that he had none, but his fear was greater than his determination and control was a loss he needed to accept.

Tony stopped the grating sounds of his own breaths, holding them and keeping his eyes tightly shut in the new, even more terrifying silence. He had to still his mind, because there was one thing left that was sure to win out over his fear. There was one thing that he counted on and trusted like nothing else in the span of his lifetime thus far.

You.

It was a struggle for Tony to retrieve his memories at first, the pain stealing his rational mind, but he was a man driven to desperation. He continued to search the caverns and corners of his mind until he found a hazy memory of your face beyond the shroud of pain, the look on your face as he left for this particular trip feeling like a fresh wound that hurt more than any he had now. Oh, how it tore at his soul to walk away that day, only made so much worse by this moment. He should have stayed home. He never should have chosen work over you, and if he survived this, Tony swore to himself that it would never happen again.

His inner visions began to shift to a happier time, because this wasn't working; he needed you to pull him from his mind before it consumed him. His eyes were still squeezed shut so tightly that they hurt, but the pain was nothing compared to that in his chest. It wasn't the pain of injury now, but rather pure, unadulterated, welcomed heartbreak.

Once he had the perfect picture of you in his mind, he could feel his body relaxing to his will; or maybe more accurately, yours. It was a well-known fact to anyone paying attention that your relationship was tumultuous. Pepper had done her best to try to bring peace between you, but she wasn't your mother, nor was she his wife, and you were both too damned stubborn to hear her anyway. She knew that the day would come when one of you would see a life without the other, and the destruction of it would be immense.

But right now, none of that mattered to him; after this, he would be different. He would be the dad that you needed and deserved. With his mind honed in on a happy memory, and his nerves beginning to soothe under the spell you held on him, Tony opened his eyes.

~~~

Tony hated moments like this, standing at the door with a bag packed and in hand, looking at you with pain in his eyes that you refused to believe was really there; you never once believed that he felt as bad as he really did when he had to leave, and he didn't know how to convince you so he didn't bother to try anymore. His life was full of business trips, meetings that extended into all-night sessions, and experiences around the world that he wished he could share, but the chasm between you both had grown too wide.

"I'll be home in two days," he called out to you, looking up to where you stood on the level above in your Malibu home. "Is there anything you want me to bring back for you? I'll be in a desert and all, but I might be able to find something-"

"No."

"Okay..." he sighed. His hand tightened around the handle of his bag, a reflex but one that conveyed how he felt when he didn't want his expression to give it away to you. He was sad, yes, but more than that, he was pissed. He was pissed that you had become such a spoiled, petulant little shit, and that he had no one to blame but himself. He tried to play it off on your age, but he couldn't deny that he had turned you into a true Stark without really trying; how could he not when it was all he knew how to be?

"I'm staying at a friend's house anyway," you announced flatly, "so JARVIS can tell me when you're home."

"Excuse me, young lady. How about if you ask me if you can stay at a friend's house instead of telling me?"

"Pfft, right," you scoffed, turning away, "I've been there all week, and you didn't even notice. Have a nice trip, Tony."

But Tony wouldn't have a nice trip; in fact, it would be the worst time of his life, and it would redefine him as a man, even as a father. He would be gone for three months, kidnapped and tortured, forced to work for a promised freedom that was never going to happen. His body was mutilated, his mind was pushed to the brink of insanity, but amongst it all was the inherent drive to live through it. It was the impetus needed to find his focus, and to find his purpose as Iron Man; but it would mean nothing without you there with him.

~~~

You wanted him to know that you had truly missed him, and that you were elated that he was home safe, so you spent Tony's first night back with the greatest meal he had ever eaten, and several of the greatest films ever made. Of course, his judgement may have been slightly askew after three months in a captive nightmare, but that didn't matter; he believed that this was a second chance at life, and he was going to do it right from minute one.

That night, with a full belly and a quieted mind for the first time in months, Tony was finally ready to sleep in his own bed again. He needed the comfort of familiarity. He needed the security of routine. He just needed sleep; the kind that didn't come with the fear of torture or forced labor at any given moment. Sleep that could be enjoyed with both eyes closed.

But even with the softest pillows beneath his head and the most luxurious sheets and blankets covering him, he couldn't sleep. He was a listless mess of a man, tiny and terrified in the big world around him. The quiet mind was gone, replaced by a paralyzing horror from flashes of those three months in hell. Anxiety was foreign to Tony, certainly this feeling of impending doom and isolation. The room around him was dark except for just a sliver of moonlight, so silent that he could hear his every breath.

As if on cue, the pain in his chest returned, and he was trembling from the cold that gripped him. He slammed his eyes shut tight and began his first panic attack; though being the man he was, he would never acknowledge it as such for several years yet to come. With his mind once again lost to him, he was transported back to that cave, alone, in pain, and hopeless. He was so frightened that to even try to bring himself together with the thought of you was a joke; he began to worry that he was finally losing his mind once and for all.

"This isn't real."

Tony pushed himself up, stumbling across his room in the blackness, barely giving JARVIS time to open the door to allow him through.

"Sir, how can I be of assistance?"

The voice that Tony had created, and one that he had known since he was just a boy jolted him from his stupor, his body immediately crumbling to the floor and onto his knees like a traumatized child facing his fear. Shaking hands covered his ears, curling his body into himself while he waited. He waited for them to come to take him away, to taunt him with drowning that never quite went far enough to do the job, or to drag him to his bare, makeshift workstation. He waited for them to electrocute him though the new chest piece that had become a part of him against his will.

None of those terrors ever came to be, and it took some time to trust that they wouldn't before he moved again. His eyes had yet to open even once, but he pushed himself up and held a hand to the wall to both guide him and to keep his balance as he moved. He knew the exact number of steps it would take, the precise movements needed to navigate items that might be in the way, bringing him to stand at your door. The gentle knock normally wouldn't have been enough to wake you, but on this night, it was as if the universe was finally working in Tony's favor, at least for this one small request, and you were quickly to the door to answer him.

"Tony?" you gasped at the sight of him. He was visibly shaking still, with beads of sweat running down his face. He reached out a hand blindly towards the sound of your voice, and when the feeling of your hand in his registered in his mind, he opened his eyes.

"I'm home," he whispered. You almost didn't hear him.

"Yes, Dad, you're home. You're safe."

In all of your life to that point, you had never seen Tony cry; you had thought maybe he came close once, but even then he played it off as being ridiculous and not his style. But now, this wasn't the Tony that you had known in all of your time together; he wasn't Tony Stark, the over-confident genius who took catastrophe in stride, he was a broken man, relying on you to help put him back together. "You called me Dad," he sighed, leaning into you to willingly accept your arms around him.

"I did. Come in here," you urged, gently pulling back from his hold to take his hand, "tell me what happened."

"Can we do that later? I'm so tired."

"Yeah, of course, whenever you're ready. I'll be here."

"Thanks," he yawned. It was as if being in the safety of both your arms and now the safety of your room, his body drained of all of the anxiety and fear, and he was left in a state of pure exhaustion. "You mind if I just lie down for a sec? I'll go back to my room, I just need a minute. I'm so damned tired all of the sudden."

You stood by and watched him crawl up onto your bed, almost childlike in his movements to find his comfort. You covered him with your blankets, bringing them up like a shield to keep whatever horrors that were attacking him at bay. Tony had taken the role of your father willingly, accepting the fears and responsibilities that came with it for the rest of his life; there wasn't a second of hesitation in you at the need to wear the role for him in his time of need. You would protect him from this as best as you could, even though you had no other means than to be there when he needed you.

Looking at him now, however, already fast asleep and nestled into the space that had normally stayed empty with cold linens, you began to believe that maybe that was the only means necessary.