While you may be marrying for love, marriage is both an emotional and economic commitment. Your potential spouse's financial situation will exert a very real influence on your life together. Your intended spouse's child support obligation -- whether it exists currently or has not yet been established -- is one area of his financial life that can affect your finances as well.
Child Support Calculation
Child support is calculated according to the laws of individual states. While each state has its own guidelines, exactly how much -- and for how long -- a parent will have to pay child support varies from state to state. In general, child support takes into account variables such as parental income, work-related child care, health insurance, extraordinary expenses and the existence of other support obligations. Typically, states don't factor in new spouses' incomes when calculating a child support obligation.
As a general rule, you have no obligation to support your spouse's children from other relationships; the support obligation falls squarely on the shoulders of the parents themselves. You do have an obligation to support your spouse. Therefore, your income and your personal financial situation can become relevant to your new husband's child support case because you affect his ability to support himself after paying child support.
Since you have a duty to support your husband, your income is relevant to determining how much money he can devote to his children from prior relationships. While his ex generally can't count your income directly, his ability to lean on you for financial support may constitute grounds for the court to deviate upward from the state guideline amount. Depending upon the laws of your particular jurisdiction, your husband's ex may be able to use his remarriage as a substantial change of circumstances justifying the modification of an existing order. On the other hand, your husband does have an obligation to support any children the two of you have together -- this means that he will have less income available to pay child support to his ex, and his obligation can be lowered.
Just as your income affects his current child support obligation, it can affect his arrears. Child support "arrears" are child support amounts that came due and weren't paid; they constitute a debt that your new husband owes to his ex. Although courts generally can't reach your income or property when collecting your spouse's arrears, they can reach it indirectly. With you to support him, your husband can devote more of his income to paying down his arrears. The more money you earn, the more your husband's argument that he needs to spend at least part of his income on self-support becomes weaker.