In general, co-signers on a note take on "joint and several" liability for the debt. This means both parties or either one of them are responsible for the entire debt, regardless of the action or inaction of the other party in paying the debt. This is one of the "dangers" or "responsibilities" of being a co-signer - you remain liable for the entire debt when the other party does not pay. Depending on how the deal is written up, you may have some right to seek recovery from your ex-husband (which may also be addressed in the divorce decree?), but this is not of concern to the lender, who typically may seek collection from both or either of you at thier discretion.
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