Roni, he needs to go to a doc, there is something not right. Extreme tiredness could be anything from fibromyalgia to cancer, from low blood sugar etc... have a doc look at it, especially since the guy is well muscled, emaning he should have a high testos. level.
To the teen poster: u were outside, that puts stress on the issue of sex, esp if u r new or relatively new to sex. In additon in another posting u said u did nto have a condom, I think in your case that it is nerves of bot issues. Plus u were tired, being an active teen it happens. But the orginal poster mentioned this guy has had this prob 4 at least 10 years, that means there is something seriously wrong.
Every guy in the world has a bad nite, including me. Any guy who denies it is full of ^&%$#! But 4 it to go on 4 years as the origal poster says there is a prob. take care,