Hi Daniel,
Thank you for your post and your question. For your husband, ideally he will see a doctor and/or therapist to be evaluated for depression. Fatigue, stress, and withdrawal could be depression; but they could also be linked to a medical condition (such as thyroid problems or a hormone imbalance). So a doctor would be the best place to start in case his symptoms have a physical cause.
If you want a self-test, the one I like is the Burns Depression Checklist at
http://www.suicideforum.com/bdc/index.html . The checklist is a good way to track changes over time as well.
I hope this is helpful to you, Daniel.
Take care,
Erin