Foreplay. Tell him it is ok to have "quickies" sometimes, but that you want to have romance too. If you can extend foreplay to even 20-30 minutes or more, you might start re-training him. It might be a good idea to have a few nights where you just do foreplay and go into it with the rule that there is to be no penetration or orgasm. Changing up your routine like this can really help things.
However, if he thinks this could be a medical problem, then seek advice from a doctor. Otherwise, I think you can have fun trying to make your love life "last longer."











