Spike gives Jack a weary glance before turning his attention dome-wards, to the projected sky, the wet depths behind it. Wasn't that long ago that he felt like if he could only break through the glass, he'd find freedom. Now, what's even the point of trying?
"...I have nothing left here."
Energy, enthusiasm... sanity. Rose anchored him, kept him on the right side of the edge even when he was teetering dangerously close during those first weeks with a soul. She gave him humanity without being human, gave him something to focus his efforts on.