I agree ... an affair is the WRONG ANSWER!!!
#1 you will be bringing yourself down to his level
#2 he could use that against you if there are legal proceedings
#3 what kind of message will it be giving your children? That lying and cheating are acceptable behaviours?
If you cheat and the marriage breaks up, where will you be then? Sounds like you are more affraid of going back to work than you are of disolving your marriage. Stop focusing on what he is doing and put the focus back on you. A job will give you a sense of self worth and independance. Sure job hunting will be tough but it will be worth it. You will learn a lot about yourself and may find out you aren't as helpless as you think you are. Worry about the "what if's" when they happen and know that he won't change until you do. Remember ... "one day at a time," "one step at a time".
*hugs*