Disappointed in you?? Absolutely NOT! Your love and the father of your children just did the dirty on you. How are you supposed to feel? We are all disappointed in HIM, not you!
The only way to get over someone is to have as little as possible to do with them, in my experience. The less you see them, think about them, hear of them, the quicker they recede from your life. I know that must be spectacularly hard when it's your husband. Time is a great healer. It's a cliche because it's true.
Also, no man is worth this. Just remember how much he has hurt you. He left his wife and the mother of his children for someone else. I don't think he's the great wonder you think he is. Good men stick by their wives and families, and if there's something about the marriage that's making him so desperately unhappy, he tries to fix it. If it's totally unfixable and he is totally miserable, then he discusses a divorce with you and is fair about it. He does NOT do what your husband did.
This might be cold comfort now, but you won't always feel this bad. You've had the shock of a lifetime. It's something everyone dreads and it's life-changing. In a way, it's equivalent to being diagnosed with cancer. Hugely shocking and your life will never be the same. So don't be hard on yourself! Inner Boudicca, indeed!
The state you're in goes to show how utterly cruel these sudden walkouts are. There is no reason he couldn't have sat down with you and gently raised the possibility of divorce, and discussed how you both feel about it, over a few months. This sudden-shock business is disgusting in its cruelty.
There are ways to go about things, and your husband chose the worst, most hurtful, most cruel way. He isn't the prize you think, and I reckon you'll feel that way in time. I read about runaway husbands and, many many months later, the spouse who was left felt disgust at the idea of taking the person back.
Sending you soft and gentle hugs. He isn't worth your love and loyalty.