They had always known, on some level. Alex more than Bobby, because she lived in the real world and he did not, but they both knew; it had not come yet, but it would. They would be alright. They could deal with pretty much anything.
Alex had known since their third month together. She had seen the loneliness and the vulnerability in him, and she had realised how this would go. She knew that she would end up loving him, despite the thousand reasons she ought not to, and she had accepted it. It was stronger than her. She felt it in the way they fell together, the way their loyalty sprung up and grew at a terrifying pace - she saw it every single day, as she began to trust that whatever insane thing he was doing was actually a stroke of genius. She loved him, and so she waited patiently, in the belief that he would eventually realise that he loved her too. This trust was not misguided.
It was not misguided, but it took him a while. It was not until she left him, although temporarily, that he realised how much he relied upon her to keep his world in order. He missed meals, forgot to sleep, wandered off on tangents that were in no way related to the case in question. His life was blurry and out of focus without her in it. And when she came back the world made sense again, and he knew that he might never find anyone who understood him like that if he spent the rest of his life looking.
So they continued, same as they always had, and they grew closer and closer and more reliant upon each other, until it was more likely that they knew what the other was thinking than not. They were together more often than not, too, as their hours stretched late into the night, and even when they weren't at work they might be having a drink together, or making sure that the other one had eaten that day, or sleeping on the other's couch after one drink too many. They were wrapped up in their life together, however disjointed and unusual it was.
And then she was hurt, and he thought she might die, and he could not imagine life without her. For the time she was gone, dead, even, his world crumbled around him. But then she was alright - battered, bruised, but very much alive. He had sat at her bedside, her small hand in his big one, and they had talked, a little, about how terrified he had been, how brave and brilliant she had been. He was so sorry that he had nearly been the reason she died, so, so sorry. She had not even blinked before telling him, straight to his face, that she did not blame him in the slightest. And when she was finally allowed out, he had taken her home. She knew her way around his apartment as well as he did - she spent more time there than she did at her own home - and he had given her tea and a quilt and an old t-shirt that she had worn more recently than him, since she had slept on his couch only the week before.
"I'm alright, Bobby," she had said, when she had seen the worry on his face. "I just need to sleep. Hand me a pillow."
"The bed has clean sheets. You have a wound. Alex, please."
Too tired to argue, she had nodded. He had helped her into his bed and got up to leave.
"Stay, please."
It was not a desperate request. It was a calm one. Even so, he could hear the layers of exhaustion and fear and loneliness in her voice, and they were all so familiar that his heart ached. So he had taken off his jacket and jeans and laid down next to her and tentatively held her in his arms, and that was the end of sleeping on the couch.