As much as he was able to, given his position, Jack tried to watch the myriad of expressions playing across Ianto's face. Jack truly loved these moments to see Ianto so completely unguarded. Each tug from Ianto's fingers sent that heat of lust uncoiling in his belly, rewarded by a rub of his tongue or a very (VERY) gentle scraping of his teeth along the underside.
It wasn't ego at all that Jack knew he was good at this -- it was the sheer desire of wanting to please his lover. The soft moans and grunts or the way he could feel Ianto tremble beneath him was the only thing that mattered to Jack. There was the slightest hint of desperation in his movements, in the way his fingers dug into Ianto's hip that spoke more volume than words ever could. It was the fear that the man he had come to care for, that he had come back for, wanted him still.
Hell, Jack wasn't sure what he would have done had it not been the case. Carried on, of course, but there always would have been that 'what if' lurking in the back of his mind. He was at Ianto's utter mercy with the way he was holding his head, powerless to do anything but rise when Ianto tugged. As if that was the greatest disaster in the world.
Following Ianto's lead, Jack rose, abandoning his erection for the time being to pressing body flush against Ianto's. That keening tone in Ianto's voice shot straight to his groin and Jack was glad for the initiated kiss -- all the better to contain his soft groan of pleasure.
"Tell me what you want," Jack breathed against Ianto's lips, hips rocking ever so slightly against Ianto's, as he lowered his head for another kiss, this one mostly teeth and tongue. In that moment, Jack would have given Ianto the world. Hell, deep down, Jack knew he would do anything for his lover, no matter what.