A.S.
Oh dear, I'm not quite sure what to offer as far as advice, but I read something the other day that you may want to tell hubby. If a baby smiles at someone, and the other person shows little response (i.e. doesn't smile back), the baby can develop a little depression. It's very important for any caretaker, especially baby's parents to be responsive to all of baby's emotions, no matter what they are. Here are some SAHDad websites that were posted on mamasource in Nov 2006 (I hope they're still available websites!) that might help pep up his routine or daily agenda with raising his son and help him connect with other SAHDs.
www.slowlane.com
http://www.slowlane.com/connecting/sahds_online.html
http://www.rebeldad.com/index.html
http://fatherhood.about.com/od/stayathomedads/
But, then again, this may be his personality due to his raising and may not be changeable. Both parents need support when raising a baby whether its thru our family or other parents. There are working Mom meetups on meetup.com if you're interested in finding something for you as well.