I, too, think you have to strike a balance. I know I really needed to talk and tell my side with my addicted daughter. She had everyone believing that she had her life together. The people that knew me well could see that something was wrong and couldn't figure out what in the world was wrong with ME.
I finally decided to open up with a few of the people closest to me. Lord knows I needed someone to talk to. Just so happened that one friend was going through the same thing with her son, had been trying to hide it from everyone and needed to talk to someone, too. So you never know.
I guess the balance would be that if you need to talk and the person asking seems genuinely interested in having an answer deeper than your standard surface answer, then talk. If you think they are just being polite, or want information for gossip purposes, then give them one of your standard answers.
Bottom line....take care of yourself and do what you're comfortable with. Because you are right that you shouldn't shoulder any more of his burdens.
Good luck. Thoughts and prayers are with you.