Work ethic vs details-oriented are two diff things. Maybe have a pull request model where you approve and give feedback?

If it's truly work ethic, then your call on whether to continue the project. Projects/startups are like romance, don't try to change the person (to each their own), or expect change to happen, just let people be who they are and decide if you want to continue given their disposition.

Be humble, be chill, and know you have your own faults that he probably has to put up with. I'm an only child. I wish I had a brother, so for my sake (lol), prioritize your relationship above your project.