Donna,
Try and remember that while your son is an adult, he is still your child and should not be brought into personal conversations/ arguments between you and your husband. I hope you have a good support system with family, friends, coworkers, but your son should not be one of your confidants. It may be tough, but I bet after the initial shock, your son may realize that your separation/ divorce is not too surprising. I hope everything works out as best it can.
Kelly