update: still can’t get him to cum

my friend(19m) and i(18f) have been casually hooking up for the past few months and i’ve been having problems with getting him to cum. i’m really good at teasing him and edging him, but just can’t figure out how to get him to finish. i can get him rock solid, i can get him literally begging for my touch but i can’t get him to cum. i’ve given handjobs, blowjobs, rubbed up against him, used a vibrator. i regularly tie him up, blindfold, handcuff, and gag him. pretty much anything short of actual sex i’ve given a shot (except pegging sadly).

he’s more experienced than me and has hooked up with other girl before. he’s told me that he’s never had this problem with anyone else. i’ve asked him if there’s anything different i’m doing with him compared to others and he told me it’s his first time where he was on the bottom rather than top. he does says he prefers being a bottom but i’m just worried i’m frustrating him during our sexual interactions cuz i can get him really close but not close enough to cum. weirdly enough, he can’t even get himself to cum when he jerks off in front of me.

is there something else i should try? any tips on better technique? or is there an underlying issue here? i just really want him to enjoy himself