There are all manner of debilitating medical conditions.
Some anatomical conditions can not only be physically debilitating, but can also bring about bouts of depression. I myself suffer from several severely damaged discs in my lower back. Over the years I have learned coping mechanisms to be able to function in a relatively normal fashion, but the pain is never truly gone, and sometimes an activity will flare up the injury and leave me immobile for a period of time. Major surgery (fusion) would likely reduce the instance of painful episodes, but there are no guarantees, and it would also greatly reduce my mobility. I have suffered some degree of depression due to this injury over the years, and while it was profoundly unpleasant, it was only as long lived as the intensity of the back pain.
Depression as a disorder causes a persistent feeling of sadness and loss of interest, it affects how one feels, thinks and behaves and can lead to a variety of emotional and physical problems. One may have trouble doing normal day-to-day activities, and depression may make one feel as if life isn't worth living. Depression isn't a weakness, nor is it something that one can simply "shake" off. Depression may require long-term treatment, and many people with depression feel better with medication, psychological counseling or both, but as with any medical condition, and especially one involving the complex organ that is the human brain, there are no guarantees.
I have known several people in my life that suffered from major depression and succumbed to the debilitating effects of the disorder by their own hand. With all of them I was devastated by the loss and saddened by the futility, but in each case I knew the pain and suffering they endured and understood their action. Not to say that I agreed with their choice, or condone or endorse it, but I did understand it.
Someday medical science may be closer to 100% effective in treating depression, but until that day there will be people that are unsuccessful in their attempts to manage their condition and choose to end their lives. I will mourn them, but I will never criticize them.
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His lack of mobility and the near constant pain make him depressed too. But his dr. prescribed something for the depression and I gave him an inversion table for Christmas and both things help. I hope you find some relief too! 
I wish they could promise better results from surgery, he would go for it in a heartbeat!
I've tried the inversion tables and in practice they actually increase the pain. I have radial tears, so inversion pulls the tissue apart and pinches nerves. The best therapy I've found is aquatic exercise. The near weightlessness relieves the pressure on the discs without pulling them apart.
We live in hope for advanced surgery. I'd do it in a heartbeat too if there was something better than fusion. 
May your efforts at managing your condition continue to provide you relief and peace.
