Ps4 don't want to share anymore?

I share a friend's game and he doesn't want me anymore. I can no longer set my Ps4 primarily because I was told that I have already activated another one. Online there's only one registered device on my side.
what happens if i disable my own ps4? Can I log in again with the account afterwards? What happens then?

You can completely deactivate all devices online once, I've done that too, it's a bit hidden in the security or account settings because you just have to click through