They need each other. There’s a reason Messi has been the primary driving force to make this happen. He’s been running himself into the ground to carry Barça, because he’s had to be super human the last few years to win games. He can’t carry that load forever, and he knows Neymar is capable of taking some of the pressure off of his shoulders.
Without Neymar Messi knows he won’t reach the heights that he wants to.
I'm personally disappointed in Neymar, I know money was a factor in the PSG move but the other motivation I felt was to separate himself from Messi and build his own castle. I really thought he could do it too.