next time you knock one out..dont cum, get to the stage when your about to climax then Stop... wait 30 seconds then do the same thing again....and again and again. Its a very frustrating process but it will get you and your dick use to the feeling and in turn prevent you from cumming quickly during sex

Helped me..but the next problem you will face is not being able to climax during sex! ( Happens sometimes to my self, normally if something is on my mind thou )

Good luck Fella