Falling through the Bifrost was really a traumatizing thing for Loki to go through, so he decided to go the only mortal man who had ever made him feel… safe and loved. Tony Stark.
The thing that no one knew, the most treasured and protected secret was that Loki knew Stark from way before the Avengers initiative. From before Thor's banishment even. The famous Iron Man had caught Loki's attention on several occasions, so he of course decided to go to Midgard and investigate, find out who that mortal was, posing as a god of metal. He had found him, followed him, sneaked into his, well, tower, and while maintaining invisibility, watched him do various things. Mostly, just tinker around in his lab and get black-out wasted. But his attitude was what attracted him more. Such a dominant, self-destructive façade, but on the inside, he, much like Loki himself, was just hurt and vulnerable. Hurt, because everyone was keeping secrets from him and doing things behind his back, and the constant denial of his vulnerability is what made him even more vulnerable. A lost soul and a brilliant mind, hidden in a body on the edge of just seizing to function. Seeking comfort, but failing to find it. Loki also needed comfort, craved it, as if it were more precious than life itself. Desperate to get to know this mortal creature, one day he decided to just show himself to Stark, and let things take whatever course they may.
As it turned out, the two of them had a lot in common, and oddly enough, they balanced each other out quite perfectly. At the beginning, there was a little problem with who would dominate, but in the end, they decided that they both would dominate, one time it would be Stark, the other it would be Loki. They were glad they made that decision as it gave them a chance to explore their softer sides, which, don't be fooled, did exist, buried under all the pressure of other people's expectations and one's own glorious purpose in life. Things were going fine for them, as Loki was just what Stark needed, and Stark was exactly what Loki needed. Their relationship was built on many levels and layers, not just physical, but emotional. They had moments when they would just want to fuck each other into oblivion, and they did it roughly and relentlessly, but there were times when just cuddling, or holding hands, or merely being close to each other was enough. With them, it was more than physical, so much more. They understood each other's pain. They were made for each other.
But then, the whole charade with Thor happened, and Loki had to take his place on the throne of Asgard, and he couldn't visit his mortal lover anymore. The burden of the crown was heavy, especially when that crown was never meant for him. He was hurting more than ever, and the only one who could console him was in another realm, and Loki couldn't visit him. He knew, it would compromise Stark's safety, and that was the last thing Loki wanted for the one person who loved him back. And then after Thor returned, changed by that mortal woman, Loki felt his heart break to a million tiny pieces. In a few days, a mere mortal had achieved with his brother what he had been trying to do in years, but he failed. He failed, as a brother, as a son and as a king. And in the moment the Allfather said "No, Loki." he knew that his life as an Asgardian prince had to end. He might come back one day and conquer it, he thought, but all he needed now was to be what little was left of himself. He needed to be able to be weak and vulnerable. And the only way he knew to do that, was to go back to Stark. He shed a single tear, for his brother, and let go of the spear.
So he ended up in downtown Manhattan, at Stark's tower, and waited for JARVIS to alert the billionaire playboy that he had a guest. Stark wasn't ready for guests, but when with the corner of his eye he saw the monitor of the security camera, black and green and gold, and red, he knew, and he immediately rushed to open the door, welcoming his guest, ignoring the fact that he had left his lab without putting a shirt on first. Bruised and bleeding, Loki leaned on the doorframe with one arm, and with the other he reached out to stroke his lover's cheek, trying to calm him down a bit.
"Tony…" he said softly, calling him by his first name for the first time, letting his voice crack and show how weak he was.
"Loki…" Tony pulled the god into a strong, crushing hug, that would've been painful, if Loki could still feel physical pain at that moment. A tear rolled down Tony's cheek, but he wiped it before Loki could see it, and instead lead him inside, ordering one of the robots to bring cotton, bandages and hydrogen peroxide.
They lived together for a while, until one day Loki disappeared without as much as a farewell, only to reappear again as a villain who wanted to rule Midgard. That's when shit went to Hell, and Tony knew there was something off about Loki and his appearance, his eyes for one, were more blue than usual, and the god acted as if he had never seen Tony or Iron Man before. Feeling hurt and betrayed, Tony refused to deal with Loki any longer, and after the whole shenanigan was over with, he let Thor put chains and a muzzle on the god of mischief and lies, The god of mischief and lies! Tony reminded himself, and let him be taken to Asgard to face trial and punishment there.
He said he didn't give a damn about what happened to the god, they might as well rip him to pieces for all he cared, but the truth was that he was the one being ripped to pieces, his heart reduced to a pile of ash in his chest, threatening to further poison his body. So he poured alcohol on the pile of ash and forgot of it's existence, slowly drinking the pain away, the alcohol erasing very memory, every touch, every kiss… leaving him emptier than ever before, but soon he couldn't even remember how happy he had felt while with Loki. At least, that's what he always told himself while gulping down the whiskey straight from the bottle, and passing out, only to surrender to alcohol-induced hallucinations of him being with Loki again, and that's all they were, hallucinations caused by heavy drinking. Or were they? It was too surreal for him to tell the difference, so he finally gave up, and continued drinking himself into oblivion, just to fall into the sweet abyss of hallucinations over and over again, forgetting about his pain, even if for a little while…