The general rule is that members (owners) of an LLC are not responsible for the debts and obligations of the LLC. However, there are exceptions to this general rule. One being that a member voluntarily assumes responsibility through a personal guaranty. The guaranty that you signed was signed by you personally and not by the LLC. Therefore, it becomes your responsibility. Personal guaranties in commercial leases are common.
Unfortunately, it sounds like you did not seek legal advice BEFORE you signed the guarantee. The LLC does not protect you for the Guarantees that you signed. Please stop trying to negotiate this yourself and get a good tax and business lawyer.
I hope this helps!
I agree with Glenn. However, I would add that if you are concerned about the guarantee, i.e., you believe you are going to default on the guaranty, I recommend you seek the advice of an asset protection attorney. Depending on your situation you may be able to protect some of you assets through an Estate Plan, gifts or other conveyances.
All of the terms you are identifying are subject to negotiation. Any business owner should have a relationship with a business attorney. The business attorney should review the lease, and any other significant contract. A good business attorney not only provides legal advice, they can also provide advice on negotiation techniques.