i will not promote, Cofounder wants equal say wo touching our banking setup in forever

We're a 2-person SaaS (55/45 split, both with day jobs at the time); he owns frontend and finance (ex-banker), I own backend and product, and that division worked fine until we landed paying US and Gulf customers who needed a real multi-currency business account, not just a checkout link. He was supposed to set it up, but six weeks in it was eight pings and a 12-day payout hold that left us unable to cover hosting, I did it myself-comparing Stripe, Paddle, and Lemon Squeezy before landing on Unlimit for SWIFT/SEPA support, live in about 4 days. Now he's resurfaced wanting full say on "account decisions" despite never touching the setup, which has damaged our working relationship. I'm not sure how to even frame that conversation with him.