Do you have sex when he has morning wood? Morning wood is at a time of maximum testosterone.
Are you on top any of the time? If you are on top, he can concentrate on staying hard and squeeze his legs to keep from going soft as fast. This may give you enough time to have your orgasm.
Have you tried Viagra, Cialis or Levitra?
Him being selfish or you perceiving it as such will cause major problems.
Does he go down on you before intercourse? He could get you on the verge of orgasm before intercourse, so you would have the orgasm during the intercourse, even if he went soft afterward.
Do you two ever have sex that is just casual fooling around, without any expectations to get to a certain level?