He had absolutely intended to continue on with the show of being in control, of affecting Jack in a variety of scientific ways, checking his nerves and blood flow and the like. To tease Jack the way he'd teased the Doctor. But in the end, desire won out. And Jack said that the Doctor could want.

He cupped Jack's face and kissed his mouth. He had intended to make it slow and pointedly scientific, but he found himself kissing him firmly, deeply. After all, what were intentions if desires were elsewhere?