In an alternate universe, Tony Stark never came out as Iron Man, even to his teammates. Sometime after CA:WS, Bucky comes to the tower, regains his memory, and rekindles his relationship with Steve.
A year later, Steve and Bucky realize neither of them have ever had sex with anyone else, and they probably won’t if they keep their relationship monogamous. When they decide they want to explore, Bucky decides to ask Tony for a one night stand, and Steve decides to ask Iron Man. Both of them bite off more than they can chew, as they both discover that they’re in love with their extracurricular lover - while still being madly in love with each other. Tony just hopes it’s all worth it, because if they ever find out it was him with both of them, he’s pretty sure they’ll never want to see him again.
The vigilante Iron Man is in the habit of showing up at a fight and disappearing again when it's done, whether the Avengers want his help or not. Steve has had more than enough of it, which is why, when Bucky finally manages to get him with a tracker before he flies off, Steve isn't going to let little things like a broken leg, an overprotective boyfriend, and a mysterious satellite deadzone get in the way of tracking him down.
Their - okay, fine, Steve's - truck breaking down on them might be a bit more of an obstacle, but at least the mechanic they've found, a guy called Tony, is nice enough to put them up - or should that be put up with them? - for a few nights while he works on repairing it.
“Iron Man likes this place?” Steve hisses at Bucky, his centuries-long witch-hunting partner and husband in all but name. “They’re using magic on humans.”
Which is illegal under the witch–human treaty their job is enforcing.
Steve would hate to shut down Iron Man’s favorite bar. For one thing, Iron Man will be less likely to date them. For another, they can’t ask the hot bartender, Tony, to bed in the interim if he’s in jail.