It is a tragic story.
It started six months ago.
Clint was not around when the announcement was made, Agent Coulson was down. Loki had killed him, and there was nothing anyone could have done. Agent Phil Coulson had died.
Clint had been under Loki's mind control and though he saw everything that had been happening and part of his mind wanted to stop, it felt right. The powers Loki mastered were incredibly dangerous.
It had been after the final battle, after Thor and Loki had returned to Asgard that Nick Fury had sat Clint Barton down and explained to him what had happened.
"Thor was detained with in the cell; Coulson was there to fight Loki off. There was so much going on, we were stretched so thin." There was no easy way of saying it. "Phil Coulson is a hero."
Clint knew Phil was gone, he just didn't know how it happened. He couldn't help but blame himself. If he had just fought the mind control harder, if he had been just a bit stronger. He could have been there; he could have protected Phil. Clint stared at Director Fury as he spoke; only registering a few words. Now that the adrenalin had worn off, he felt the magnitude of what was being told to him. Phil Coulson was gone, forever. His Phil, lost, and there was nothing he could do about it.
SHIELD had a funeral, no casket, cremation (as per SHIELD regulations). Clint could not take being the grieving widower, as everyone saw him to be. He and Phil had been together. That next week would have been there 4 year anniversary, but that doesn't matter anymore. Clint sat in the front, and had to listen to everyone tell him how sorry they were for his loss, how much Phil had meant to them. These were not things Clint wanted to hear. More than anything he wanted to be sitting at home arguing over whose turn it was to do the dishes, or trying to talk Phil into getting a dog (even though he knew it was a bad idea, it was still fun to bicker about it). Clint wanted to be anywhere, anywhere in the world at that moment, just not there.
SHIELD had a memorial set up for the Agents who had lost their lives during their service. There were a surprisingly large number of names on the board. Phil's name was added to that wall, there was a star after his name, a mark of honor. Clint would spend most nights in the air vents, staring at that name. He memorized the font, the size, the shadows the lights cast off the raised letters.
After a few months, everyone on the Avengers began to worry about Clint. It is not that they thought he should be over Phil in that time frame, but they noticed a change in him.
At the archery range, Clint would spend hours loosing arrows. Then suddenly he wasn't anymore.
Clint would spend time in the air vents, hiding from the rest of the world. Then he didn't.
Clint complained about headaches.
And after Natasha forced him to a doctor's office, the team learned what was wrong. Clint had a brain tumor, in his hippocampus. Clint was losing his short term memory.
He was going to need surgery. The surgery would run the risk of him losing large portions of his memory and possibly his motor functions, but it was a risk that would have to be taken in order to save his live.
During recovery it became clear to the Avengers that Clint would recover nicely physically. He regained his ability walk and talk, and eventually he was back up to par with his shooting and archery. He, however, did not recognize his teammates. He remembered his childhood, he remembered the circus, he even remembered being an assassin, but he did not remember SHIELD, he did not remember the Avengers, and most tragic of all he had no idea who Phil Coulson was.
It pained everyone. Such a beautiful love story was gone, and there was no one left to remember it.