Hey Peter,
Here's a couple suggestions:
--Make sure your parnter comes first, from oral or manual stimulation. Then you won't feel as pressured while having intercourse.
--Practice "holding off" your orgasm while masturbating, picturing Margaret Thatcher in a thong or whatever
--Get a cock ring at your local sex shop. It fits over the penis and testicles, constricting blood flow out of the genitals. You get hard, and stay hard even after you've come. But make sure you don't get too carried away!
Good luck!