Keep changing your technique, different hand, different grip; stimulate only your glans, stroke only with your finger tips, feel your shaft engorge under your skin as the core becomes firm. Train yourself to enjoy the sensations within your cock instead of achieving ejaculation/final orgasm. You may discover the pleasure of multiple orgasms, or at least the the thrill of being able to maintain your erection for longer time periods. Experiment with developing your erection through Kegel exercises; i.e. creating an erection without touching your penis. My personal goal: achieving erection and orgasm without ever touching my penis. Nowadays, I will edge for approximately two hours, time permitting, before I permit myself to ejaculate. My erection is the firmest it has been for numerous years, and I feel sensations throughout the full length of my shaft.
Ask your partner to try different stroking techniques, also. You may discover new things you enjoy, like not moving your hand on your shaft while your ejaculate pulses through your cock. There are also things my wife have has done with my cock which I've never been able to duplicate myself. I will never stop trying.