We are attractive to each other and we have great sex, but he can't cum. Why?
I think first you need to ask your boyfriend NOT to masturbate for a whole week! So he can build up a bigger load. So when you do have sex... it will be hard not to cum. I can always tell when my boyfriend has been masturbating all week... his load is much smaller and weaker. Also hes not rock hard. Hes always hard...but he gets incredibly harder and bigger when he holds back and waits for me. The sex is much more intense. Sometimes he cums too fast though...and it upsets me.
There are many possible causes. Age, feelings of shame or guilt, tension, pressure to perform. those are only some of the emotional and mental causes. Then there are some physical possibilities. Like obstruction of the tubes, low hormonal balance, scar tissue. etc. He should be checking with his PCP. - - Gino -- - Good luck
Just to add to the answer by escortagino, he may masterbate too much, not uncommon in younger males, he might get defensive if you ask so instead ask him to do it for you because you want him to then you both can enjoy.