She's always there to catch him when he falls.
His hand is still warm with her touch when he throws himself from the roof of St Bartholomew's Hospital. The memory stays with him for the next two years, it's one of the very few things that pulls him though the constant fear and torment of his self-appointed mission.
He's so near to spiralling into old habits after John's wedding – the siren call of drugs too strong for him to resist – when she slaps him back to his senses, and he's secretly grateful to her for that. It's this memory that helps him as he's fighting for his life, the pain of a gunshot wound searing through his chest.
She's there to pick up his pieces after the final confrontation with Moriarty's twin brother, panic surging through him as he considers how close he's got to losing his friends one more time. He can't make out the soothing words she's whispering in his ear, but her lips are soft and he's desperate for everything he's denied himself for so long.
It's surprisingly natural for him to catch her in turn when he finds her slumped on the bathroom floor, crying her eyes out. He wraps his arms around her, and she gives him a watery smile as he tucks her in bed.