You probably will not be able to "force" the bank to add you to the account, but usurping the LLC bank account was improper.
It looks like your LLC has come to an end as a collaborative effort. You need an "accounting" (what you have, what you owe and plans to resolve). It is not too early to look for a business litigator if your negotiations to wrap up your business do not proceed amicably.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
Your next step should be to find Washington State Counsel knowledgeable in our case law regarding minority interests in limited liability companies and to review the LLC's operating agreement to determine what your rights are and to determine if the agreement allows him to take this action unilaterally. Generally, one of the purposes of an LLC is to limit the liability of members, but if you personally guaranteed liabilities you can still be on the hook and that is another issue entirely. In short, you need counsel to determine what the real issues are for you as to risk, and, whether or not you already gave him the right to make this choice.