Meg take care of yourself. Well wishes for smooth procedure and speedy recovery. Your children are old enough to help out around the house and tend to your needs. I would try to rely on your H as little as possible.
You definitely need to set clear boundaries. Whether or not you reveal your knowledge of the A to H is a personal choice but I'm sure the OW fiance' at some point if he hasn't already told the OW that he has contacted you. Once that happens OW will share drama with your H. You need to know that "drama" on either end will pull them closer together. The less drama you create will not add more fuel to their fire but be the bucket of water that snuffs it out.
M's survive A's all the time - look at this board. Many make it to recon but many LBS's decide they no longer want the M. Remember there is no deadline... this is your time table. You've taken a lot of steps to look inward already and are finding you are stronger than you thought. Whether this M survives is no longer up to H but completely up to you. You hold the power.
