it seems to me that if you are 'good friends' and otherwise happily married, then possibilities are open, even if they are not the best ones...but 13 out of 21 years is a lot to overcome in that area of a marriage.

Stress and smoking & drinking can easily be root causes, but libido is a multi-faceted aspect of a person, based on genetics, personality, health, history, moral attitudes and several other things...no easy answer, as you already knew...,,,I suspect that, after awhile it is just easier for him to not try to add one more 'coping' to life...Some things depend on momentum and 'familiarity', and although no one really "forgets how", like riding a bike, it seems a bit scary to try after long layoffs..

I wish I had more ideas....just try to share and care about the things that you DO enjoy.