Her eyes closed briefly as he described his grief. It felt almost like she could see him there. Holding on to the edges of his sanity, grasping for some form of relief. Anything. Even an end to it all. She knew how close he'd come to tipping over the edge the first time around. But he'd pulled himself back together. Gotten himself a comfortable new job. Of course, there he hadn't had Jim Moriarty constantly shoved back in his face. Kidnapping him, haunting him (literally), and any other number of things. But still.
Back home, he'd had her. In the beginning he'd fought so desperately not to let anyone in, but she'd wormed her way into his life with a serious determination a weaker John Watson hadn't been able to fight. Here, though, she hadn't been around for most of that. She'd only arrived at the beginning of his recovery, and her presence and what it implied had thrown him off, she knew.
"You're stronger than you think, John," she finally said quietly. "And better, too. It's good that you have people who will help. Who will defend you. But I think you'd manage." Without even considering what she was doing, she reached out, resting a hand over his knee. "Sherlock loves you because you do the same thing for him that they did for you. That you're doing for Florence now. You pulled him back. Made him remember how human he can be and why it's all worth it. That's just who you are. Even when it's hard, even when it hurts. He's the brains, but you're the heart. And every one of us knows it."