I'm sorry for your loss. Its always difficult to lose a friend. Survivor guilt is inevitable. While I never knew Setzer, it seems the good guys have lost another from their ranks.
There may or may not have been many things you could have done or did not do. Setzer was his own person, made his own decisions for good or ill, and this most final of choices was his to make.
As one of the living, you might consider taking a lot more vitamin D, perhaps even consider an injection. Fish-derived omega-3 may help treat depression. Best to check that they do not interfere with any ongoing meds.
If you live far northern country, there is a possibility of chronic vitamin D deficiency, especially if you spend a lot of time indoors. While fair-skinned people recover somewhat over the summer, non-whites do not recharge on vitamin D from the sun as quickly; asians and blacks in particular, because of their darker skin.
Some nordic caucasions cannot process omega-3s from vegetable sources such as flax to the EPA and DHA very efficiently, so a fish oil such a cod liver oil might be the best omega-3 winter supplement. Cod liver oil delivers a fairly complete package, but be wary of the cheaper stuff that uses artificial vitamin E as a preservative.
Deficiency peaks in the spring, after the long winter in the northern hemisphere; its takes about 6 months for regular intake to really soak in, although some people find immediate results depending on how bad off they have been. Most people don't get enough omega-3s anymore in their diets.
Remember your friend in a good, honest way, as the friend he was, and that will always be with you and something positive to live for and share with others. http://www.psychologytoday.com/articles ... izophreniahttp://www.stripes.com/news/special-rep ... s-1.153434http://www.umm.edu/altmed/articles/omega-3-000316.htm