I understand what you mean Math in your last sentence, but in general I feel the worst time for a faithful spouse is when they suspect nothing, while having to deal with strange behaviour at home. I always feel the worst is over when you know, because at least then, you can make some decisions.
And in your case SandSad, I would prefer you to think of yesterday's revelations as an almighty blessing in disguise; you were in fact in a far worse position last week when you believed your H could change and that you could "fix" this.
Hopefully, you know now that he is beyond redemption. I doubt he could be faithful to anyone. If he is to be believed about who this is, he wasn't "faithful" to her either, was he?
This has got absolutely nothing to do with you, but all of us can see that your life would be an absolute misery if you stayed with him. You know how much I worried about your mental health at the end of your last thread and queried why you were suspending making a decision. I respect you for your reasons, but if you set yourself free from constantly wondering and obsessing about who he is texting or meeting this time, it will be like a weight lifted off your shoulders.
What are the practicalities to consider now? Could you move closer to people who can help? How will you deal with the children, especially your DS who was manipulated so shamefully by your H? I'm sorry I can't remember all their ages, but how much did they know about why you were having problems?