I’m sorry you find yourself in this place also.
Whatever you do, do not buy a house with him. I really believe that works be a very bad idea, as not only does that tie you to him but also if he is getting into debt, it is not ideal at all.
Can you look at getting yourself somewhere to live with your son? Even if it’s renting.
Your partner can sort himself out by himself. If he truly wants to… he can do it.
I’m in a similar position except we have a young child together. I’ve decided that he needs to sort himself out – I can’t make him quit and I can’t tolerate his behaviour, which is paranoid, violent, delusional, aggressive and volatile etc. He has tried to quit by himself and falls back in very quickly. I’m fed up with it. I’m just waiting to get rehoused.
Put yourself and your son first.