I’m sorry this is happening, and I’m sure the “giving up at 40” is just an idea, but in reality it doesn’t work that way and it’s not that easy! If he wanted to stop then he would do it now.
Aggressiveness/mood swings make them appear as monsters. My ex partner is more interested in that drug than his own kids. He is always so angry, and you’re right “angry at the world” and don’t seem to take any responsibility themselves. It’s always blaming others and just nastiness!
Keep your guard up because you need to protect yourself from HIS chaos. It’s all full of darkness.
I don’t know if these men ever get back to being who they once were! It’s just so sad so very sad