I think there’s one sign you can see in healthy co-founders: if they want to catch up every day.
Being a founder and a leader is … isolating. There’s often no one else as CEO especially that you can really share the day’s and week’s challenges with, not really.
Ideally, that would be your co-founder.
When you see that relationship, the end-of-the day meet-up, every day. That’s when you see 1+1=3.
Conversely, if you don’t really want to meet every day … It’s probably somewhat broken. Try to fix it. The longer you wait, the tougher it will be.