I suggest you contact the lender and ask them to remove your name. Depending on the current credit-worthiness of the other person that signed for the loan (your ex) they may or may not grant your request.
If the lender won’t remove your name, the next option is to arrange to have the loan repaid in full. Perhaps your ex can borrow from another lender without you as a co-signer and use that money to repay the debt.
Unfortunately, the fact that you are no longer partners does not relieve you from the obligation to repay the debt.
I suggest you contact the lender and ask them to remove your name. Depending on the current credit-worthiness of the other person that signed for the loan (your ex) they may or may not grant your request.
If the lender won’t remove your name, the next option is to arrange to have the loan repaid in full. Perhaps your ex can borrow from another lender without you as a co-signer and use that money to repay the debt.
Unfortunately, the fact that you are no longer partners does not relieve you from the obligation to repay the debt.