It wasn't that he didn't know people, didn't talk to people. He had always been fairly social and that hadn't quite disappeared. It was rather that people didn't know him.
He could see it in their faces, the incomprehension. Tom, as dear a friend that he was, the only one who knew the truth, could never comprehend that there were horrors beyond what he knew. He didn't see that the 'awesomeness' of being a spy and saving the world came with the crippling weight of responsibility and guilt for every life he didn't save.
Blunt never saw him at all. He saw a tool, which no matter how useful it had proven to be, was still in the end, expendable. He didn't see Alex as an employee. No, employees were given benefits. They were paid. Employees signed contracts with vacation time and health benefits and security clearance and colleagues. No Blunt didn't even realize that he was a human, or at least he didn't let himself.
Mrs. Jones saw him as a child, albeit one that had been through a lot. She didn't believe he could understand the implications of anything. She treated him with a firm hand, making decisions without asking for his advice, and feeling sorry for herself when the guilt finally caught up.
And Jack, oh Jack didn't understand that he had no choice. She saw him throwing his life away and dragging her down with him. And she'd never have left, no despite all that she hated about what he did, she'd always stayed by his side, loyal to the last.
But what none of them realized was that it wasn't the death that got to him. It wasn't the fear, the pain, the guilt, or the responsibility. No, it was the loneliness. And, despite all that he still talked to people, he knew that, when it came down to it, he was alone.
Every mission he went on, MI6 proved this to him by failing to turn up when called, by not standing on his side. His Uncle had died, and with him, he took the false image that the government had his back. And with that realization, came the fact that he was alone. Brecon Beacons showed him that adults were petty and untrustworthy and didn't care that he was smaller and younger than them. Working with the CIA showed him that other countries were no better than England. ASIS continued the trend by adding their name to the list of agencies that manipulated him, and Ash, his godfather ash, showed that betrayal could come from anywhere at any time. Yassen, who had been the cause of his loss, the only one who had seemed to be on his side, had been put there through deception and had left with a bullet in his chest. And then Jack, stupid, stupid Jack, went and got herself killed and Alex knew, as he had always known (there was a reason he jumped out the window after all) that he was alone.
As he left with the Pleasures, he did it knowing that they would never understand him, and the world of intelligence would never let him go. And he waited knowing that one day, maybe in a few months, maybe in a few years, they would come back, calling him calmly to check on his bank account, telling him that he was all they had. And he would come back, because he was alone and that meant, at the very least, that he had nothing left to lose.