I had a long overdue positive interaction today. I think we've both realized that if we don't work together on this we're finished. So that's a good start.
I'm going to take your advice about doing something that's not work and then try to have a conversation later. I have noticed that in the past he can totally reject an idea but then accept it a few days later.
I have also had more success previously with presenting a course of action as me attempting to support him or his goals. My ego gets in the way of doing that too often though. It's been tough.
I think I may also have some internal insecurity in regards to him trying to hog the limelight whenever possible. I like to think that I'm above feeling that but I do often have to check myself to make sure I'm doing things for the right reason and not as some kind of passive aggressive retaliation.
Get away from the office and have an uninterpreted "strategy session". Sometimes leaving town and relaxing a bit helps. Do something fun, not business related for a night then the next day have a conversation. Start with facts he can't dispute that are not personal. Something you can both agree on. Like, can we both agree that the business is sinking and only has X months left? If you can agree on that, the next question is what do we need to change to fix it? You can bring up some of the issues without personally attacking his style. A la "I think we need to listen closer to customer feedback and focus on revenue generating opportunities within their feedback"
I've worked with a lot of personalities that sound familiar to your co-founder, the trick is planting the seeds so they think it was their idea/or they were at least apart of the ideation process - when really it's exactly what you wanted them to do and your purpose for engaging in the conversation. Not everyone can just be directly reasoned with or is receptive to direct feedback.