Lauren:
I am by no means an expert either but ten years ago, I was working on a Master's degree in psychology and working at a school for developmentally disabled children (my husband at the time left for someone else; I had to quit school and take a full-time job and have never been back to school.)
I personally believe that all illnesses, whether mental or physical, can have multi-dimensional causes because God made us as multi-dimensional beings (body, mind, spirit.) I believe that if something goes wrong in one area, it will affect the other areas as well, and the cause of such things can be both spiritual (demonic) and/or physical/psychological. However, I do believe that if someone is willfully choosing the wrong things, it can, of course, make things much worse.
I have struggled with severe depression all my life that has manifested in a multitude of symptoms (including a suicide attempt that caused the loss of a few friends--I prefer to think that, although of course, my choice was wrong, it also helped me see who my true friends really were--not as an excuse, but as a testimony that God can use even our worst choices for a better purpose.) I have also heard the arguments that I wasn't a Christian, was going to hell, had no need for medication, etc., and was in and out of a combination of counseling and meds for at least ten years.
It has taken a very long time, but one of the things I've found out about myself is that I was borderline Type 2 diabetic--for some reason, my system does not metabolize insulin in the way that it should and so I had been living my entire life with excess insulin constantly running through my body, which creates a lot of stress and imbalance. I was just diagnosed with this last year because the doctor I went to approached my issues from another perspective and ran some tests no one else had even suggested. I am no longer on any anti-depressants, but just one medication for high blood pressure and another to help my body process insulin properly (I also had to make changes in my diet) and I can honestly say I'm doing better than I think I ever have been in my life. I will probably be on these medicaitons for the rest of my life (I'm 35), but I had no idea that something like this might possibly be a major contributing factor to my constant depression. I have also noticed that my depression is always worse if I eat a lot of processed sugar, so I know that for myself, cutting back on sugar and carbs (I don't drink but I know alcohol would be in this category too) makes a major difference in my moods. It may not work for everyone but it's helped a lot in my experience.
However, during the past 4 years, I have also spent a lot of time becoming involved in most anything my church had to offer as far as counseling, various ministries, serving on the prayer team, etc. I had to make a lot of hard choices, letting go of old crutches and moving in the right direction, stick with the right choices consistently, and it wasn't easy, but I have no doubt that it is a combination of all of these factors that God has used to help me get on the right track.
You and your husband are in my prayers. I know he needs to work out the pain of losing his first wife and adjusting to his responsibility to you as your husband now. I pray that his heart will soften to make the right choices and accept the help he's offered... and that these hard times will bring you closer together, and of course, more importantly, closer to God, in the end. And I pray that God will comfort, strengthen, and bless your desire to be a supportive, loving wife to your husband. God doesn't forget that you need support as well, so I sincerely hope you can find others in your area going through the same issues so that they can encourage you without judging or criticizing.
Blessings to you.