Oh dear, honey. I'm not a doctor and I would never try to diagnose anyone on a message board but I have a 24 year history of Depression myself and it sounds like you've got it. You must seek help IMMEDIATELY. Do not delay. See a qualified psychiatrist or psychologist if you can. You may need to take meds. Improving diet and exercise will help of course but sometimes people need meds. (Therapy helped me restructure my thinking but nothing took the "pain" away until I started taking medication. It's the only thing that's worked for me.)
Everyone needs to talk to someone objective and "unload" too. Believe me though - one thing is 100% for sure - you're worth a WHOLE LOT more AS YOU ARE to your wife and kids than any old insurance policy! You may not feel that way right now - but it's true!! Hang in there and get some professional help. We all need help sometimes!