It sounds like your best way forward is the route of a less critical role for this cofounder. At least in the short-term. Longer-term, I would think the other

It sounds like your best way forward is the route of a less critical role for this cofounder. At least in the short-term. Longer-term, I would think the other cofounder(s) would at least be considering the "removal" (buyout, whatever) of the this cofounder. No one wants "dead weight" eating value of a company they aren't contributing to. It will only cost them more later. Or, if the other cofounder(s) don't seem to care, maybe that's a sign you should move on yourself. Maybe you should bring up the subject of "dead weight" with the CEO to get a sense of the situation?