1. Is your team making progress? Because startups have fewer people and resources, your founding team needs to be effective producers.
2. Do you guys trust each other to have your back? An example they gave was how two cofounders were arguing over equity. Instead of arguing that the other guy should get less equity, they were doing the opposite and insisting that the other guy should be getting more. And from that, they knew there was some underlying trust that drove their decisions.
Seems like this guy is breaking that trust repeatedly by doing weird stuff. And continues to do it after your confrontation. This sounds like a situation that will only get worse.