Because you made a personal guarantee, both of you and the corporation are jointly and severally responsible for 100% of the loan.
That means the bank will dun both of you. If he refuses to pay any, you must pay it all. If he pays 30% and then declares personal bankruptcy, and the company pays 10% of part of its chapter 11 reorganization, you pay the other 60%. That is what "jointly and severally" means.
There's no consideration for the percentage of shares.
Normally the entire point of a corporation is that you are not personally liable for anything more than the investment you initially made (for which you were compensated with shares). With a loan guarantee, your personal liability also includes the amount of the loan.
Watch out; when you guarantee or cosign a loan, often the very first notice you get that the loan is in arrears is when you get a negative mark on your personal credit report. As far as the bank is concerned, part of your responsibility as a guarantor is to remain "in the loop" with the other borrowers, and know that the loan is in trouble. The bank expects that you, under your own recognizance, will intervene with your loan payment ASAP. At least before the loan becomes 30 days past due (the point at which credit reporting bureaus will mar your credit). If you do not do this, they will be heartless.
When you are forced to make someone else's loan payment because of your guarantee, they now owe you, and you can sue them. Good luck collecting. However the corporation could give you more shares instead of cash, for what that's worth.