sorry, forgot to add about rejection:
rejection sucks. there seems to be some stigma out there that when a girl rejects a guy it is not a big deal....but when a guy rejects a girl...something is WRONG!
not ALL guys are horn-dogs and are DTF 24/7. Its shocking, but true. When he says "no" to sex, do you think there are reasons? tired? work? stress?
Guys brains are weird. Lets face it....for girls, all we have to do it open our legs. sometimes we get off....other times we don't. Guys are expected to pop wood and fuck to kill at a moments notice...and if they don't, something is wrong!! am i fat? am i ugly? did i do something? does he not love me!? etc...etc...etc...If a guy is distracted or preoccupied with life, it can be hard for them (no pun intended) to "get into it". This seems to happen more when they get older and/or mature (do guys ever mature??

).
also, some guys just don't have a high sex drive or a sex drive that everyone thinks dudes have. society has seemed to ascribed this horn-dog mentality to ALL MEN, but in reality...its not all that realistic.
The best thing you can do it talk to him about it....dont pressure him...just ask. He may just be tired....his mind may be miles away....or, he may be a little embarrassed that he is a quick shooter? maybe introducing some things i suggested above will peak his interest?
try not to feel bad when he says "no".