1. The terms of your shareholder’s agreement
2. Your state’s law
3. whether the minority shareholder is being bought out of his ownership interest or merely terminated as an employee.
Often, employment and ownership are linked--for example, if your employment is terminated, you are deemed to offer your shares to the company for sale.
If that's the case, you have a strong argument for not having to continue to advance funds to a company that you no longer have an interest in. Yet another factor will be the terms of the credit line agreement: whether the guaranty is contingent on you remaining an owner of the company or not.
But it's best to review your shareholders' agreement (assuming you have one) with a local attorney. Minority shareholders do have rights concerning fair treatment and you may have negotiating leverage to get yourself off the credit line if it turns out the majority shareholder hasn't done right by you, which could be a violation of your state's corporate laws.