What Causes A Person To Be Depressed And Make Verbal Abuse?

I'm concerned about my husband. Weve had marital problems for years. He is generally a nice, hard working guy, but has had many affairs and is quite controlling. I attributed this to episodes of drinking; however, we are getting a divorce and now he is unreasonable to talk to. He changes from being quiet and calm, can't sleep, obcessing about things especially sex, and is quite depressed at times talking about how he is a failure and everyone is better off without him. He then goes into this "hard working" mode and starts new projects and seems like he's driven by gears. Im scared to be around him anymore due to the verbal abuse and threats he makes if I leave him. He has talked about almost getting hit by a train to sending me pictures of himself sitting in his truck late at night. Im very scare for my kids but cant find any support groups or support from his family. They blame me for leaving him and think he is just depressed.