I agree with Lexie. The mind is just as important in sex as the penis. If he's white knuckling it to stay sober, and not in an actual recovery program, he is probably battling demons.
That doesn't mean you have to accept this as your way of life. You're young, and deserve a healthy sex life. You deserve a partner who seeks true recovery. I'm glad you've started with AlAnon. You will find more answers as you attend meetings.