How do I deal with a haunting memory my son's father?

I loved him very much but he was so depressed and it didn't show until after our son was born. His sadness spread to me to the point I had to seperate from him to keep from joining him on a journey to suicide. I didn't know he was suicidal until after we seperated. He committed suicide and I have spent years trying to recover from the guilt and anguish of it. I have been to some therapy and on a mild anti-depressant for a time when it was unbareable. I thought it was getting better but I still feel he is a huge presence in my life... haunting me through memories and dreams... It has a profound affect on my family when my husband wants to know everything and I hate him for it. This is a personal matter to me entangled with guilt and resentment for decisions I made in the past. Please help if you can. Sometimes I can't breathe in the life before me for the sadness that overcomes me.