He may not be able to have enough blood trapped in the penis to keep it erect... so this might be just the kind of situation that will profit from Viagra, Cealis, or Levitra. These drugs can really be fabulously effective-- the only thing is you need a doctor to prescribe them ( DO NOT GET THEM OVER THE INTERNET) so that you can be sure that he is a good candidate for them ( ie will not have a bad reaction to the drug because of other medications he is taking or because of heart issues, etc). They really can make a great deal of difference- and if he is excited and willing , this will just make it easier to sustain the erection since his desire is already present. I would talk about this together and see if he would be willing to go see a doctor and see if the doctor believes this would be right for him. If it is, I think you will be very pleasantly impressed with what it does for his ability to make love to you.. Pepper Schwartz, Ph.D.
if he is overweight, smokes, drinks and/or takes certain meds (such as bp meds or an antidepressant) it can affect his ability to maintain an erection and ejaculate. could even be his testosterone level which can be resolved if he has a blood test to determine if this is the prob. sounds like the same situation i have w/my bf 'cept he is in his mid 60s (i'm 51)...we literally can not have sex at nite coz he cant keep it hard and when we do have sex in am, he only ejaculates maybe 1/2 the time. he had triple bypass surgery & takes bp and cholesterol meds. he quit smoking a few months ago after 50 yrs, and seems to be doing a lil better tho..
keep tryin different things tho - and good luck to you.