Brief Answer:
Please talk to him regarding what you want 
Detailed Answer:
Hello
In today's world of modern medicine, sex is never all over, till the time you want. You can't force someone if he does't desire.He has high level of desire ,( though if the desire level has changed dramatically just recently, there can be some underlying cause like psychiatric problem, 
brain tumour or testicular growth), so he indulges in 
masturbation. Orgasm is between the ears, not between the legs. Discharge of semen ( between the legs) is associated with feeling of intense pleasure( between the ears) One can have either of these without the other. so may be, he reaches orgasm withmasturbation but  not with vagiinal sex. Feeling of failure to do so has reinforced his thinking . Itispossible to correct this by appropriate 
counselling, provided he. is ready for it . It can be done on  line as  well You have to tell him exactly what you want. I may tell sexual pleasure is not limited to vaginal sex only, there so many other ways as well. so I think., he is erring in assuming that he an not have orgasm . If hehaswith masturbation, he an have with vaginal as well.
Dr Saatiish jhuntrraa