If you agree with the tax assessments, go ahead and contact the IRS and set up a payment plan. But, if you were married to him any of those years, you might reduce your collective tax debt if you file married filing joint, the downside is it would become your debt too.
Depending on his financial situation, the resolution with the IRS is either an installment agreement (like a payment plan), and Offer in Compromise, or having them declare the taxes currently not collectible, due to hardship. You would need to give the IRS person a financial statement, usually on a Form 433-A or similar (except, if your husband owes less than $25,000, he can get an installment agreement without one).
You could contact a lawyer if you feel more comfortable, and one might help if you are eligible for an offer, but otherwise, a lawyer isn't going to get you a better deal than you could get by yourself. A local enrolled agent might be better, though.