[Incredibly desperate is the answer. They've both seemed to enjoy making these five days as hard as possible and those hands on his ass are enough to make him surge desperately against him, whimpering desperately into another kiss. It's just the latest teasing tough he's had to endure in the last five days but at least this time he knows it will be more than just touching.
He can hear Jack's comment and laughs breathlessly, feeling a bit giddy and overwhelmed as it sinks in that this is real, it's really happening, he's really watching them do this. If he wasn't already hard that thought would be enough to get him there and he rocks forward, knowing Spike can feel the press of his erection against his thigh.]