I, truly believe, it's a normal reaction to a deep hurt. It's also, part of the grieving, of a relationship. Intellectually, one can tell ourselves, that logically, that's not true. You were the one, that was good enough. You were the one, who contributed enough to the relationship. And, perhaps, because, I'm on a limb here, you aren't the type of person, to lay blame on others, first. ((<---which isn't a bad thing, per se; just means, you are more likely to look at your own flaws, or even question things that aren't flaws, first.))

You mentioned, you don't drink. And the person he went running to, sounds like she enables his poor choices, and his dysfunction. So, it's not, so much that you aren't a good person, wife, mother; it's he and you, lost connection, in his mind, at least.

I've heard, it expressed to me, as far as my exh goes; all he had to do, was seek treatment, and not take his anger out on you? Some people, don't know a gift, when they have it. You, being that gift. He squandered you, and all he had/has.

Let him, one day, ask these very questions of himself, where you are concerned, some day. When, all is lost on him, to him.

It's grief, plain and simple. I feel for you,