Is it legal for a cosigner to be responsible for all the signers debt during a marriage?

im going thru a divorce (2 years now) and it has been nothing but hell to say the least. im ready for a divorce and the ex keeps changing her mind on the agreements. this time she wants me to be responsible for 20,000 debt we bought when we were married on a truck that has been repoed. (20,000 is the balance left). i was wondering even if i sighned the agreement for the debt owed if it was legal for me soley to be responsible. like i said i was just the cosigner she was the original signer. any help at all