Phil Coulson should have never gone on vacation.
Granted, he had been busy doing his job with SHIELD, but when he decided to actually use his vacation days after the whole Convergence incident? Hydra happened. It happened fast, and everywhere. And he was damn happy that he hadn't been working when things went down- it let him go into hiding, go underground, avoid the fire. Normally, he'd have been one of the ones to stand and fight, to support the Captain the whole way. But Steve still didn't know he was alive. And his own agents had been off duty, and he had to make sure they were safe first and foremost.
They were all fine. After the organization had been torn down, Phil had called Maria Hill, asked what happened, demanded an explanation to how Hydra had gotten in so deep. She had explained that it had always been there- the Nazi Doctor who'd been there since the organization's start had been turned into an AI, had slowly turned the organization for peace into one for anarchy and death. She told him about how Nick Fury had been killed while giving Steve information that helped them intervene and stop the crisis. She told him that the job was done. Go home, she'd said, SHIELD is gone.
As much as he hated it, he had listened to her. Kept in close contact and kept all of his gadgets, yes, but he went into hiding. He'd rented out an apartment and began looking for a new job, scouring the internet and newspapers. FBI or CIA may be nice, they were close to what he had been doing, but they didn't feel right. He could work for Stark, but even Stark didn't know he was alive.
Deciding on where to apply took longer than his next payment for rent, and he quickly found that unless he decided on what new career he wanted fast, he'd be out of cash. So he decided to put out an ad for a roommate to help pay off the rent, to keep the cash coming in while he finished sorting out his life. He hadn't expected the only person to call in to be someone who should have been dead.
Even with the longer hair, Phil recognized Bucky immediately. Only a true fan of Captain America would have also delved into his team as much as Phil had, and though it'd been a while since his last visit to the memorial, he still had the memories. That, and the fact that Bucky had been on the news for attacking Steve & Co. in public.
Imagine his surprise when he actually took Bucky in as his roommate despite the lack of funding that he'd been hoping to procure (and well, the lack of an amiable atmosphere.)
Phil Coulson should have never gone on vacation.