He remembers guarding Loki while he slept.
He remembers other things too; painful things. Killing people on Loki's orders, some of them people he had known, people he had worked with in the past. Strangers too, guards who just happened to have the bad luck to be in the wrong place at the wrong time, between Clint and his target. Half-destroying the Helicarrier on Loki's command, part of a distraction to keep SHIELD and the Avengers from tracking down Selvig and the Tesseract before the portal was ready to be opened.
He remembers answering every question Loki ever asked him, in detail, a word-vomit flood of information about SHIELD, Fury, Phil, Natasha, Hill, the assorted freaks of the Avengers Initiative. He remembers the pleasure he felt every time Loki smiled or patted his arm or otherwise indicated approval of his service. He remembers how good it felt, to be the thrall of the god, how willing he felt to do anything asked of him. It hurts to remember it now, that pleasure, that easy acceptance of the role Loki had given him.
But the memory that hurts him the most is the memory of guarding Loki while he slept. It was something he'd often done for Nat, and sometimes for Phil when Phil was able to be with them on a mission instead of lurking in the background somewhere. Guarding them, so they could sleep soundly, entrusting their own defense to him. Guarding them, so there was someone there to wake them if one of their nightmares started.
He'd seen that Loki wasn't sleeping; couldn't sleep, so wired on fear and desperate energy that he could barely even sit, could not settle, could not surrender his safety for even a moment's rest. Saw how pale and unkempt the god was beginning to look, the darkening bags under his eye looking more like bruises, the restless nervous energy that had him pacing endlessly, hands never still, always busy. Remembers the missions where Natasha looked like that, so desperately in need of sleep, yet unable to rest, unable to slow or stop.
He remembers ignoring the wary, wide-eyed look Loki gave him as he drew him aside finally, into a small side room, where he had put together a simple pallet out of folded cargo blankets on top of a row of crates. "You need to sleep, sir," he said, and indicated the primitive bed. "We've got several hours until we need to leave for Stuttgart; I'll guard you while you sleep."
He remembers the way Loki had stared at him; surprise and disbelief and a deep, deep suspicion. "And why would you do that?" Loki asked finally.
"Because you need to sleep, sir. I'll guard you while you do; there isn't anyone coming through that door without meeting one of my arrows, sir."
Loki studied his face, perplexed. "Why?" he asked after a while, the word a demand.
"It's what I do for my teammates when they need to sleep, sir. I stand guard so they can."
Loki laughed, once, briefly. "And is that what you see me as? A teammate?"
"Yes, sir. And you need to sleep, sir."
Loki shook his head, but then gave in and moved to stretch out on the pallet, looking amused. "Wake me in two hours."
"Yes, sir," Clint said, and had sat down on the floor, his back against the crates, bow and already-strung arrow resting on his legs, held loosely but needing only to be pulled before it could be released. He'd heard Loki's breathing settle, heard it begin to slow toward sleep. Felt fingers touch his nape, toying briefly with the hairs at the back of his head, the same way Natasha usually did, as even Phil did once when particularly punch-drunk on lack of sleep. Felt Loki's fingers close in a loose grip, wound into his hair, holding onto him so that he couldn't move away without disturbing Loki's rest.
He remembers how peaceful it felt, to sit there with Loki's hand touching him, checking his watch at intervals and otherwise not moving, until it was time to wake Loki, for events to begin to move again.
He guarded Loki while the god slept, and it's the most painful memory he has, because it was the one thing he did by his own choice, not because Loki asked it of him.