Fortunately you know you have been an enabler. Now you need to deal with it. Unfortunately you gave him the money that would have been a nice downpayment for you on a new home. The years will continue to go by. Make the best of it.
It sounds like he has some type of disorder that no amount of help from you or collaboration will help, he needs to realize he has problems and needs to get help and it sounds like he is not there.
Get out, you may see differences in your DS as well if you can find a positive male role model for him. It won't make your DS's issues go away but it may calm down some behaviors.
Planning at this point is important to get out, don't worry about buying or renting you can decide that later. Now it is important to get out as emotionally intact as possible as a family.
I would absolutely leave for this. And I would not be going collaborative. I would be getting a bulldog lawyer to get back that 45K your mother gave you as a way out of your situation. I also would cancel the car insurance on every car that is not yours and stop making meals for him or doing anything else that financially benefits him. I would rather be a single parent than do it all alone AND be harmed financially. What must your credit be like if you are left with bills you can't pay at the end of each month. I would absolutely start making a plan and getting out.
I would leave simply because I was unhappy. The financial stuff probably comes up in any marriage. Just be prepared to have separate finances from any spouse you acquire in the future.
But seriously. If you don't love him, that is reason enough to leave. Have you had counselling together?
Also, collaborative divorce is awesome. depending on what state you are in, I could point you in the right direction of a good practitioner.
Please do not give him a heads up or any other kind of warning about what you intend to do.Get as much financial info on him as possible cause he sounds like the kind of man that would hide assets so that he can plead poverty in court.I agree with a previous poster,stop paying for anything that does not directly benefit you or the kids(why should you pay his insurance?)Don't cook,clean or do his laundry and as far as custody it seems to me that it would be in your son's best interest to have only supervised time with his dad since he can't understand his problems.When you do go to court make sure that supervision and parenting are included in the orders.And also don't leave the family home until your lawyer says to cause it means that you acknowledge that it is his and legally you don't want to do that.If you and the kids can't have it then it needs to be sold and the money split.He has already got a financial advantage,don't give him more power.Speaking personally i have been much happier since i split with my kids father cause i don't have to worry about trying to please someone who isn't trying to do the same for me.
Yes, I would leave if I were in your shoes. Make an escape plan, line up your "ducks", and get out. Don't give him notice ahead of time--I agree w/ pps on that.
In the meantime, why on earth are you paying for 5 cars? Can you sell some of those if you are on the title? Drop the insurance on that and pay only yours, cancel his phone if you're paying it, same with cable and any other non-necessities. That will give you more $ to save up for your escape! I would totally start craigslisting everything you can and putting the $ in your account or even in cash and hidden if there's a place it could go that he won't find it.
I would find a roommate or apartment or something---sounds like you will have to postpone your actual physical leaving until summer, so be it. Save up for a downpayment on a house if possible---being a first time home buyer is not as intimidating as I thought it would be, and you might qualify to be considered as that if the two of you never went through the process together.