Are you writing code yourself or are you 'non-technical'? Founders don't 'manage' other founders. You sound like a non-technical who has some idealized view of how software is made.
I'm writing the code myself, how I could get the code is undocumented otherwise?
That's what I'm saying too, I don't want to "manage" but he's being actually lazy.
It could be a motivation issue if it was a decline in work quality. If you're like most startups, and you're not profitable right now, it's important to quickly become profitable. Having a constant stream of real validation of your business's value is very important--make sure you're making the right product. Otherwise, there's no shame in pivoting or dropping the dead weight--but in my opinion that's like firing a canary because it stopped chirping.
Sorry mistircek to say this - great partnerships that we read about in the press (i.e YouTube, Google, etc.) don't happen to all of us aspiring entrepreneurs. This happened to me and it was one of the most challenging times in life. We worked for more than a year on a project. Looking back, I wish I let that person go 10 months earlier, but the optimist/humanist kept nudging me to keep giving it a chance. If you're a lot more motivated, it's better to be a sole founder, build traction, and then find another co-founder & give that person less equity. You deserve that much more equity if you're the one hustling the most.