Whether it's because of some internalized homophobia or for other reasons, Clark is weary of getting fucked by Bruce even though he's enthusiastically loved all the frottage, blowjobs, intercrural and whatever else they've been doing.

Thing is, Clark really wants it and demurs in the face of Bruce's seduction that allowing him to slip him just the tip of his cock (after having allowed him just a finger maybe) but he ends up begging for more verbally or physically (pushing back, spreading his legs, moaning shamelessly) and a good time is had by all!