I'm sorry you found this out, but as you know, I'm not the least bit surprised.
Just a couple of things for you to consider:
A) If he's buying her a ring and rushing to finish the divorce, it MIGHT be because she's pressuring him or he's eager to move on, BUT - it could mean she's pregnant.
B) Don't assume that she KNOWS he is married. It's possible he's been lying to her all this time as well and that's why he doesn't want the two of you to have contact. (Of course, it would be normal not to want contact between your wife and mistress anyway, but.....)
As for his business - I'm not a lawyer, but it's my understanding, that if it's a sole proprietorship based on his labor alone, it may well not have any intrinsic value. This is a question for your attorney.
Also - the separation date may be useful as a bargaining chip, but if he's already being super-generous - again, it may be worthwhile to grab the money and run. Don't confuse standing for the relationship with [protecting you and your kids financially in a divorce - the two are not mutually exclusive.
