I 25 and my partner 56 have the problem that if he has "bad day" and needs to take the pill, he is about 6 of 10 times done chance to unable to get an orgasm/to cum. Maybe it is that we are like mentioned earlier, passing the 15-20min in act or then it is the pills. This does not directly mind me but i feel he thinks that he does not sexually fill my needs if he does not cum.
On a "good day" we usually play for hours with many sweat swiping and hydrating breaks. Our grand finale is to aim for cum-together, what usually happens.
Did some digging, cialis can affect prostate and actually seems to be medication for overgrown prostate. So there might be relations for being unable to cum. Talking to doctor definetly clears it.