He gives himself one second.
One second to not care about anything else.
The world is literally ending right in front of his eyes. Thousands are dying with every heartbeat. Gigantic ancient sentient machines slicing into buildings and bombing entire city blocks, and for just one second, he doesn't care.
In that second, he looks to his left, and she's there.
She's looking down at Anderson, who refuses to leave the soon to be doomed Earth, and he knows that when his second is over he, too, will mourn Anderson's decision, but he has this one second until that will happen.
And one minute from now it will hit him that his family is there on Earth, and he's safe on the Normandy, broken free from Earth's gravity, past the line of reapers, out of danger and headed to the Citadel. There wasn't time to go get them or anyone else's families, and communications to Earth are severed. He will hope that they were able to get away from the city and find shelter somewhere long enough to wait out the invasion, until he can return with all the fleets in the galaxy at his back. Then, as soon as the Earth is secure, he'll find them.
But in this one second, he doesn't think of them.
All he can think about is that standing next to him again, after so long, is Shepard. And they're on the Normandy, together, just as it used to be.
In his second, thoughts surge through his mind, the whole of their experiences together, from Eden Prime to Ilos to Alchera to Horizon and just minutes ago back on Earth. The slow but steady fall for her, the desire of their few but passionate nights together, the utter devastation of her death, the disbelief of her return, the regret of his words the last time he'd seen her.
It's all there just during his one second, and his heart stops beating, his lungs stop breathing.
But he knows there's much more important things to think about than his own feelings, and as hard as it is, when the second has passed, he tears his eyes away.
And a moment later when she vows to come back for Anderson, he looks to the man who is every bit as much his own mentor as hers.
Anderson's eyes flicker to his, and they share their own second.
It was Anderson that lifted him out of the hell he was in for months after losing Shepard. Anderson knew, he was the only one that knew what happened with Shepard, because that drunken night when Anderson dragged him back to his quarters rather than have him thrown in the brig, he'd confessed it all. He'd talked and he'd cried until he passed out, waking up a day later and somehow, ready for duty again. And now something in Anderson's eyes tells him not to waste the precious few days that might be all they have left.
He nods back, in silent agreement with the Admiral.
"I'll help her. I'll watch her back. I'll be at her side. I outrank her but I'll follow her orders again. I'll do what I can to win this fight and help save the galaxy. I'll support her and give her someone to be human with. I'll beg her forgiveness but stay with her even if she never gives it. And no matter what comes, I'll love her."
It's the best he can do. His peace made, and a ship to secure, Kaidan Alenko turns and walks away to give Shepard her last seconds to say goodbye to Anderson, and watch the Earth burn.