If Spike gets off on being with the living then being Jack is going to be a full-on banquet for him. Jack's so alive he's practially shimmering with it, hot and vital and brimming with energy and verve. Well-honed muscles working against him, blood rushing through his veins, hot breath puffing into Spike's mouth as he kisses the hell out of him.
And yeah, he's at the point now where he's given up on the idea of doing anything other than continue fucking himself against Spike's hip and his hip against Spike's erection until they both come. And if that doesn't do it for Spike, he has plenty of tricks up his sleeve to help finish him off. For himself, though, it really isn't going to take much more. There's only so long a guy can hold out when he's getting what he's been wanting for so long.
He shudders as one roll of Spike's hips hits just the right spot, and groans breathlessly into Spike's mouth. "Fuck, Spike! Oh, fuck!" So, so close.