Get my ex off my back!

I left my abusive ex husband just over two years ago. I left most of my possessions behind, and I left him a car and half the money in our joint bank account, and a very fair and equitable divorce agreement. I have since mostly rebuilt my life and put all this behind me. But he has one last way to get at me: a student loan I made the mistake of co-signing for him. He agreed to be solely responsible for paying it as part of the divorce decree, but he defaulted on it to the tune of $5000, which is wrecking my credit, and they could take further action against me. He is doing this on purpose to hurt me, even though it’s hurting him too. They have offered me a waiver to get my name off of it for $1600, but I need to pay it by the end of this month. That will totally empty my bank account. I own a small business and I usually make enough to get by but this will literally take me down to zero. I just want this to be over. Please. Help me get to a place where I can forget I was ever stupid enough to get myself into this position in the first place.