Is it illegal to hold money in my bank account for someone else?

My boyfriend owes a substantial debt to the county for child support as well as a few judgments to others. I believe he is under reporting his income to avoid paying these debts. (His argument has something to do with being a self-employed 1099 employee instead of a W2 employee. He's claiming that when the court asks about his income, he is only obligated to report his income after his written off expenses.) Is it illegal for me to "hold" money in my bank account for him so that his account will only reflect his reported income? This money would be used to pay our joint living expenses. If this is not illegal, would I then need to treat it as if it were my income and report it as such to the IRS and other governmental agencies?