Legal Question in Business Law in Georgia

What is "his part?" If you are "freelance," and presumably an independent contractor or independent business, it is your responsibility to pay your own taxes. Your failure to understand how taxes work is no reason the other party should pay more. If this is not the correct situation, you need to re-post and be far more clear.

By freelance, I assume you mean you are not an employee. If so, the terms of the agreement will control. If not addressed or there wasn't one, they would only be obligated to pay the total amount agreed to.

If you're "freelance" I assume you're a 1099 independent contractor, which means you pay your own taxes, and there is no "his share." So unless he agreed in writing to pay you extra amounts to cover your taxes (and that extra payment would also be taxable to you), he's not supposed to pay them. It sounds like, before you continue in business, you need to take a few days off and meet with a CPA to discuss the tax ramifications of your business, and then meet with a lawyer to properly set up your business and draft your agreements.