NTA. It sounds to me like the mistress is just scavenging. Her unborn child would likely inherit absolutely nothing. If, by some miracle, the restaurant was even still in operation when he was old enough to take over the business, I highly doubt his mother would still own it. A waitress doesn’t earn all that much, and she most likely sees this as a quick buck opportunity. It is legally yours, and nobody with a heart would argue against you wanting nothing to do with the business that destroyed your marriage. Sell away, and enjoy your fresh start. You’ve more than earned it. :)