There is no easy answer--being part owner, even a fifty-fifty owner, of a business does not by itself make you a coequal signatory over the business's account. Instead what matters are factors such as the business form (partnership, corporation, LLC); who has what authority in the business (e.g. you can own half the business but yet not have an operational role); what the documents establishing the business provide; and how/who set up the accounts in the first place.This would be a good matter to discuss with your divorce attorney (if you don't have one yet, get one); bring with you alll documentation pertaining to your ownership of, investment and role in, and authority over the business and also relating to the bank account. If the bank acted improperly, such as through your husband's friend, you may be able to sue them.