The way I view this scene isn’t Jon being inconsiderate or not understanding what Jay’s going through it’s more of he knows Jay’s hurting and caught up in all these feelings but he doesn’t want him to say or do something that he’ll regret and will hurt him even more. Especially since Nia’s family is still alive, if they were to die, it would hit even harder and turn into a “why did all of that even have to happen” moment.
And as for him asking Jay to move and start a new life with him:
Coming from personal experience of dealing with a traumatic life event this year and someone’s there trying to comfort you, I view this more as Jon panicking.
I view it as a moment where you or someone is freaking the fuck out because something irrevocably terrible has happened and a person is wrapping their arms around you frantically telling you “it’s going to be okay it’s going to be okay it’s going to be okay” trying to calm you down as best they can while the adrenaline is pumping.
And seeing as Jon just dealt with a traumatic experience himself, he probably doesn’t know how to comfort Jay in a way that would help at the moment, but wants to find a way to make things better in the end. Plus he’s trying to hurry and fix the mess Waller made since he had a huge part in it👀