Sorry to read that you are still making excuses for him OrchidLady
You simply don't know as a fact that there is no OW. Your ex lied to you about his relationship with the woman who allegedly died recently. Remember, when he was seeing her on a professional basis and then left you and said he was going to live with her, you would have said then that she was just a friend and that there was no affair. Astonishingly, you still say that now despite him telling you recently that there were months of secret meetings and encounters you knew nothing about. The alleged presence of her husband and your blind denial about his ability to be unfaithful to you seemed to get in the way of seeing the truth then, but it's incredible that it's stopping you now.
The fact is, he has ended the relationship even though it should have been you ending it years ago.
Why would he do that?
Why would he give up a life with someone who enabled his alcoholism, his drink-driving, his refusals to have sex and his untreated depression?
I'm sure he will want to come back when he needs mothering again.
But with any luck, he will stay away for good and realise that he doesn't love you in the true sense of the word and that this relationship hasn't been fulfilling either of your romantic needs. Also that it's a destructive relationship in which to raise children.
I'm sure you'll take him back if he asks and will again put your relationship with him above your son's needs again. Which is terribly sad, but a natural progression from the denial you are in at the moment about this relationship.
Similarly, I have the feeling that you're hiding a bit behind your son's illness and the inability to get out and do some shopping, in order to get your ex to come to the house again tonight. Your son is 12. Is he really so ill that he couldn't have been left while you nipped to some shops? No neighbour that could have kept an eye on him? No facility to do some online shopping?