When a person backs up a loan personally, even if the loan is in the name of the corporation or LLC, that person is responsible for ensuring the loan is paid. Since your son is personally liable for the loan, future credit grantors will want to know that he has the potential to be required to make payments on that loan and there could, therefore, he could have less available income to pay the new credit card or loan. You should consult an attorney licensed in your State for specific advice on the LLC aspects and to review the mortgage documents to determine yours and your son's obligations and responsibilities.