I don't think having a label is any help for you. If you are willing to help your partner, I don't even know that he needs to be reading here. (What I really mean is, that I wish I had a friend reading here, recognizing me, and helping me so that I wouldn't feel any need to read/post here.)
I think it's great that you want to help. You can read up on AVPD and learn to recognize the situations that prompt feelings of rejection and/or withdrawal.
If you recognize what hurts your partner, you can try to avoid doing that yourself, and when you see someone else's behavior having that effect, you can show your partner that you care and draw him out when he starts to withdraw.
http://www.tljones.co.uk/apd/apd.htm
Above is the best site I have found in assembling the most information in one place. Yes, I'm over 40.