Have him go down on you or finger you untill you are close and then have intercourse.
Or you could do the start-stop method. Having him stop when he gets that climax feeling and then wait until it passes to start again.
He should see a urologist for other options and to see if maybe something is wrong.
18 and 29. Sick.Why wont my boyfriend stay hard?
fwhy does my boyfriend loose his hard after a few seconds?