I believe that emotions can be classified as helpful or unhelpful. The helpful version of depression is sadness. Sadness happens when there is a loss. It is helpful because it can push us to take some action. But we can also turn sadness into depression...
When my wife left me suddenly and unexpectedly after 30 years of what I thought was a great marriage, I was sad. I was very sad. It was, as described in 'The Journey From Abandonment to Healing' (a very helpful book by Susan Anderson), shattering. I had choices at that point: take action, or refuse to accept the reality of the situation.
It was tempting to refuse to accept what happened, with self-talk like "This can't be happening", "She must come back", and "I can't live without her." But I grew up with a depressed father. I knew I didn't want to go that route. It was difficult but I chose action.
* I asked for help from friends and relatives, who responded very lovingly.
* I saw my counselor and asked him for words that would be helpful: he gave me "Your happiness doesn't depend on her."
* I did a daily grief journal, which changed into a gratitude journal about 2 months after the breakup.
* I stayed in my healthy routines of eating, sleeping and exercise.
* I also hung up my daughter's painting which has the words "The sun is always rising somewhere."
If I had refused to accept the reality of the breakup I could have become bitter, but "bitterness is a paralytic" according to Sherlock. Paralysis is one of the symptoms of depression. I am still sad about the divorce, but I am not depressed.
Two websites that can be helpful:
A Moodscope member.