Spock's mouth, his kiss, were hot. Jim was not interested in delineating the different uses of that word in this context. He was deeply interested in kissing Spock, in the breach in Spock's defenses that allowed his tongue entrance, in the new/familiar taste and feel of him.

He was also interested in the reaction of his own body, marked before and growing now. Obviously he knew about female arousal, had been on the other end, but... It was weird, feeling it.

He thought, as his hands ran up the length of Spock's thighs, that perhaps he should start wearing underwear.