Some states, California for example, provide that a new spouse with income, cannot be held liable for the support of a step-child except under extreme circumstances. Your State may have similar exemptions. However, for the time being, and for purposes of financial safety, set up and maintain separate savings and checking accounts. That way, your funds do not become commingled with your husband's, and a court, should the question ever arise, will always be able to calculate whose income is whose and where the funds came.