I have to echo what some of the previous posters have said as far as not pressuring him. I was in a situation like this in my early 20s, except I was the one who suddenly had issues. I always had a very healthy libido and the problems started with a genuine medical issue- I got ovarian cysts and sex was horribly painful. I was nervous even after the cysts resolved, and then my BF started making comments and I just ended up shutting down because I felt so pressured - it was basically horrible performance anxiety. Eventually the whole relationship fell apart.
I'm not saying that sex isn't an important part of a healthy relationship, but I wouldn't consider it the most important, or even in the top 5. My last relationship was with someone who was flat out lousy in bed. I was willing to look past that because he was great in almost every other respect. Granted, after we broke up, I did joke around with a few of my close friends that it was a sign that I wasn't meant to have to settle for bad sex for the rest of my life, but that's a different story
Try to be patient and give him a bit of space to get his confidence back.