The risk is that you comingle your assets after marriage, and the IRS seizes the assets to satisfy the back tax obligation. If you keep your financial affairs separate, including filing separate tax returns, you should be able to protect yourself. Your boyfriend should address the debt by either agreeing to a deferred payment arrangement with the IRS for the debt, or requesting an offer in compromise. If he can reach an agreement about the debt with the IRS, there should not be any collection actions for you to worry about. I hope this helps.
Sign up to receive a 10-part series of useful information and legal advice about the divorce process.