After mediation, we agree to pay back $40,000 Home Equilty Line of Credit by half, but he withdraw $55,000 himself. How Can I do

Without knowing what your mediated agreement says about about how if at all either party may draw funds on the line of credit, I can't say whether he breached a contract with you by doing so, or whether you have a cause of action against him for that, for money damages. Sureley you should have had an attorney of your own review any mediated agreement before you signed it. If you have not already -- please imediately inform your bank that you want that line of credit frozen, that you did not authoize the $55,000 loan. That won't get you the $55,000 back however. Please use any means you have to retain a good lawyer immediateley and bring that agreement with you.