Ouch, sorry about your mom. I know breast cancer is a terrible diesase. It also run in my family gene too. I always get breast check up every year just to be on the safe side.
You lucky your mom willing to forgive your dad. Lot of married people I have known not too forgiveable to for give a cheating husband. It's rare. But I am sure it would be a rocky road to take time to heal the marriage and the trust issue. You are more lucky to be more forgiveable than I am. 
