I read your story as it was recomended to me because our situations were so similar.
I'm sorry that you are still feeling guilty about this, even though have no need to, but you cant help the way you feel.
The fact that he left has hasnt even battered an eyelid about it, even years later is the biggest kind of rejection you and your son can have. It hurts. For years.
You are still hurting at the lies, deciet, rejection and another million other things so it's no wonder all of your drive has gone. Your dreams have been tossed away and shattered without a care in the world like glass on tiles and it's such a horrible thing I wouldnt wish it on my worst enemy and your trust in everyone has been quickly erroded away by the actions of those who should have help you or at the very least recognised the shit you have to deal with.
Yes you have savings and a cottage that you sold and it may help financially, but money doesnt help you mentally try to recover and start again emotionally.
Indifference is the most hurtful way to act towards someone and that is all he has shown towards you and your boy. Knowing that not just your husband, who was supposed to be the one to help support you in these situations but everyone else in your circle of people that you knew..well and truly couldnt give a shit. As long as it doesnt affect them, they dont care.
How are you supposed to deal with that hurt, rejection and anger when you have to keep a lid on it in front of your son? You have no-one to scream at, cry with and no apology. Just a short sentance which was used for the divorce.
It's no wonder that you are still all over the place and will be for a long time yet. The only thing you can do is the thing you are doing now. Take it all one day at a time, do what you need to do, enjoy the up days and wallow in the down ones. When you are ready, you can do a course, or start writing again, a job to earn a living with.
Until then, just keep wading through that mud.