He can see that spark light up, however briefly, and he's more relieved than he thought he'd be to see it. And if it takes sharing some of his past to help Spike engage again, then so be it.
He shakes his head. "I'm okay now - here. I've got Ianto. But back home - those new memories they stuck in my head? Almost two years since he died, and okay, I'd finally made my way out of the bottle, but I wasn't exactly skipping around sniffing the roses either. And the first six months or so, after he died? I spent pretty much all of them either inside a bottle or someone else's bed, just trying to forget."