He's as reluctant to let go of Spike as Spike is to move, and it really is mostly about empathy and having been there himself and knowing just how much having someone there who understands can help.
He nods at the explanation for not wanting to go home, remembering his own desperation to be anywhere but Cardiff after the events of the 456 and losing almost everyone he loved there, but gives Spike a bit of a look at wanting to sleep in the graveyard.
"I promised Ianto to make sure you're okay. You sure you wouldn't prefer a bed somewhere? Plenty of empty apartments here, after all. Hell, there's even a spare room in ours if you want?"