The way Alex's demeanor shifts the second Blunt enters the apartment is such an amazing detail. Because maybe minutes before he was trying to not completely break down with Mrs Jones but the second Blunt walks in Alex is calm and defiant. The sneer he gives Blunt in that moment is so telling of how Alex feels about Blunt. We all keep talking about how important it was for everyone else to treat Alex the way they did but no I haven't seen anyone talk about how Blunt treated him.
From the beginning Blunt was harsh and used every dirty trick in the book to get Alex to do what he wanted. But for the first time Blunt is finally faced with actual repercussions for not listening to Alex or anyone else. Because Scorpia is killing anyone they want just to make a point and Alex is working with them. And then when they get a hold of Alex Blunt but no choice but to be honest.
He couldn't manipulate or force Alex into anything, he was literally begging Alex for any answers he could give because he was truly desperate, and that I think also helped Alex just as much as the kindness and grief everyone else felt for him. Because it forced him to really look past his anger for how Blunt had treated him and the anger for the deaths of Ian and his father, because for the first time Blunt had to treat him like a person and it helped break Alex out of his spiral just as much as everyone else did.
This is also why I felt like the ending fit so well. In the end Blunt had no choice but to finally trust Alex completely and tell him the truth, and honestly I think Blunt realized that his lies and his pride were part of the reason that not only did Scorpia grow back but Alex was so easily caught in their web. I also think that in the end he knew he wouldn't be able to ever tell the whole truth to anyone like he needed to, so in order for the department to do what it needed to and for Alex to stay on the right path he had to leave.