I feel like a major reason as to why John feared losing Arthur so much during season 4 (outside of the other obvious reasons), was because he already believed he had lost Arthur. That Arthur finding out about John making Faroe an orphan, is such a horrible betrayal that it is inevitable that Arthur will leave him.
Season 4 John feels like he is desperately trying to make amends, and reckon with how much pain he has brought Arthur, either purposefully or incidentally. But is very limited in how he can accomplish this because, he’s lying to Arthur, and has the deal with Kayne to priorities. So all of John’s solutions are very cold and survival focused. While he’s having to deal with his own capabilities wavering. John is scared he is no longer reliable to actually protect Arthur, or fix this mess. John feels like he’s desperately trying to disprove he’s a “monster” or that he hasn’t changed. While reckoning with the bone cathedral, and the fact that PARKER HAS ONLY BEEN DEAD FOR A COUPLE MONTHS AAAAAHHHH.