I'm no pyschiatrist, but he sounds clinically depressed. The 'great ideas' he is having is an escape from having to deal with the everyday. Impulsiveness is also a sign of depression quite often.
I'm sorry you have to see a loved one go through it. Sometimes I really think it's harder on those around you than the person that actually is suffering from it. It sounds like he (and you), have been through a lot in life and his reaction sounds pretty understandable. Men get PND too and a having to adjust to a new baby when you are already emotionally fragile is probably not easy for him.
No advise really, just to love and support him, he will need you soon. But you can't force him to do anything until he is ready. Just take a deep breath and wait. I'm so sorry you have to go through this.