SA, I know that you want to be "fair", but you have to look at the entire picture. You were a wife, mother, companion and you might as well say his mother as well. Aim high for the settlement to give you room for negotiation. Don't settle for less... Fair doesn't always work out to be fair to individuals going through a divorce. You are entitled to 1/2 of everything and don't settle for less than that.
As far as I'm concerned and I'm sure others will chime in, the ow doesn't deserve one dime of your share. Who gives a rat's @ss about what the OW wants or needs? She isn't the one that stood by your h during your marriage. Go for the gold and plan to negotiate just a little bit. If he's as desperate as we think he is to run from you and the marriage, he just might settle w/you quickly and give you what you want.
P.S. Fair to him is all for him and nothing for you....so don't feel guilty about going for the gold.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
