Tell him to relax,eat healthy,exercise and stay away from alcohol and drugs and he should be fine.
Keeping an erection has several possible solutions.
I have found that the herb called Yohimbe (the one made by Twin Labs) is very effective in keeping erections for long periods (even sex more than once )
This is bark from the Yohimbe tree. It originates in africa where it is used in tribes to get men erect and horny. The brand from twin labs comes in 200 mg tabs and I find one is totally enough. Taking two gets me super horny but also sacked out hormonally. Source Naturals makes a formula which is very good for male drive too (called Male Response) it has less Yohimbe but other things in it too which help a lot. I have been taking that one lately cause I don't like the wacked feeling from pure Yohimbe. It is very good. I can last forever (the other night I did it for 3 hours with my girl -till 5 am !!!
The other thing which is proven is that a healthy body and good heart will help with strong erections too (which I have)
Hope this helps !
C