Mickey was a fair hand at computers.
Scratch that, Mickey was brilliant at computers.
Hell, he'd even used his battered home IBM to remotely fire a missile straight into London. He literally saw the thing sail past his dirty window, sleek and deadly, and disturbingly like a UFO.
Well, he hadn't done it all on his own, but in that moment of triumph it didn't matter.
After the roar of the missile had passed, panic got sucked into that vacuum of pride, and he realized what he had done, and what it might mean for Rose.
And, he'd thought reluctantly, for the Doctor.
But the TARDIS had disappeared from London with two people in it that day, and Mickey was left with a disk containing a virus and a heart that he tried to tell himself was used to getting broken.
That was how it always was, Rose and the Doctor popping in and out of his life and dragging him into their intergalactic war games without seeming to intend to do it. He really tried not to get involved, but it always came down to Rose giving him that certain look that made him feel like he still had a chance with her. And then she would look away from him, over at the Doctor, and her face would change, and he knew he didn't have a chance after all. He thought he would give anything to have someone look at him like that someday, and later he thought that maybe he knew Rose loved the Doctor before she knew it herself.
Rose came home alone in the TARDIS once, crushed and full of helpless rage, and he squashed his jealousy, but not his concern for her. That day, he helped save the universe with a big, yellow truck.
They came back from that, but the Doctor was different, and not just his looks. He couldn't say exactly what it was that made him ask the Doctor if he could travel with them on the TARDIS, but he definitely felt something of the hunger for adventure that Rose must always feel every time the Doctor calibrated the ship. Rose was unhappy that he was there, but for once Mickey couldn't bring himself to care. She and the Doctor had brought their fair share of unhappiness and disruption in on his life; let them suffer the same for a while.
So they traveled.
In a parallel universe they saw an advert of Rose's dad, larger than life, which was odd 'cause Pete'd been dead for so long and Mickey's earliest clear memory was from the day he had died at that wedding.
Seeing Pete got him thinking about his old Gran, who'd broken her neck tripping down the stairs in her flat, because he'd been too lazy to fix that torn corner of carpet. So when Rose decided to go call on her dad, despite the Doctor's emphatic statements that this Pete was not in any way her dad, Mickey slipped away to go see if this Gran was still around. His heart warmed a bit when Rose gave him a knowing look before she set off, the Doctor trailing in her wake.
His pulse pounded in his ears as he knocked on that old door he knew so well, and he didn't care that he was weeping in the middle of the day out on the street when she cupped his cheek in her strong brown hand, seeing his face with her touch. It was perfect, but she called him Ricky and he knew that there was another him here in this universe as well.
Of course he was abducted at that exact second, by people who also called him Ricky and threw him into a white van that smelled of petrol and sweat.
And that was how he met his other self, who turned out to be London's most wanted, which he thought was pretty bad ass before he'd learned it was for parking tickets. He wasn't really surprised that even in another universe he was pathetic, but he secretly wished he could have managed to be just a little bit cooler.
Ricky died just after Mickey had met him, and Mickey had no time between the running and the screaming and the gunfire to wonder if he'd be permanently scarred by seeing the death of someone who was, essentially, him. But it made him very angry that Ricky had been taken out so easily by these metal bastards that the Doctor called Cybermen. It made him even angrier when he found out that their steel bodies contained wholly human brains, harvested by force from the people of this world. He held that anger close to his chest, and let it warm his leaden heart.
So when their little band of survivors - Rose (thank God), the Doctor, Pete, Jake, Mrs. Moore, and himself – planned a counter-strike against the Cybermen, Mickey made Jake (who was obviously grieving for Ricky) take him to the blimp to help destroy the transmitter.
And that was how Mickey saved London, saved the Doctor and Rose and Pete, and killed a lot of people all at the same time. It wasn't a good feeling, and it hit him in the gut a million times harder than when he fired that missile in London a million lifetimes ago. A slick of triumph, love, and joy floated like oil on a deep pool of loss, and he looked into the Doctor's eyes and knew it was the same for him, but vaster and deeper than he could possibly imagine. It occurred to him that the Doctor was in some respects very much alone, despite what Rose said.
When Pete broke the moment by saying that these Cyberman factories were in cities all over the world, Mickey swallowed that sick feeling of his, storing it away to examine it later.
He had already decided he wasn't going back.
There was a world to save, and Mickey had Jake, and a battered white van, and he was a fair hand at computers.