First of all, be open minded when asking for advice. You don't have to take it, but you don't have time to be slap-fighting with people about the way they've said something. It's a distraction. You have an emergency, and you've asked for help. Take it.
My advice: You need to make a decision about whether or not you should stay in your marriage. I suggest making the decision, and then don't act on it. Let it sit for a while, and see how it fits. You've been doing this for thirteen years. A few more months won't kill you.
It sounds like you're in a hurry to grab up this guy before some other woman does, and you're willing to get divorced to do it. That is so Desperate Housewives. I understand the desire, but I want you to hear this: no man is worth changing your standards for. If you're contemplating things that you would never normally do, you'll regret them.
I think you're pretty firmly in place as The Martyr in your marriage. Think long and hard about how it would feel to be the Bad Guy.
And what about the hard, cold reality of economics? Are you ready to support yourself? Do you think you could get a fat divorce settlement out of your husband if you decided to leave him? He sounds like the kind of guy who might dedicate the rest of his life to punishing you. Don't bank on your high school friend. If you do this, you have to be ready to face the possibility of doing it alone.
I got divorced last year after being with someone for 11 years and being The Martyr for the entire duration. I am now back with an old flame. I am sympathetic to your situation, and familiar with some of the potential pitfalls. Feel free to PM me if you want to discuss, but not if you want to argue. I got enough of that from my ex.