He lets Jack press him down until he's resting on his forearms on the desk, bent over and perfectly positioned. There will never be a time when he doesn't find this unbelievably hot. Just being in place like this is enough to turn him on, start to get him hard with no more contact from Jack than that kiss and the hand he can feel on his back, warm through the pink fabric of his shirt.
"I need you." He means it than just an answer to the question. He needs Jack, needs every step of this. Even if he was physically ready from Spike he would still want Jack to do this.