In s19 Simmons states how Grifs paper work was processed a hour ago, not filled out, and he makes discharging Grif the first thing he does, as if this is something he has been planning.
And that makes me think that this wasn't a sudden decision Simmons made, I think he had this planned out for a longggg time.
Grif was never quiet about how much he didn't want to be there. It was never a question of if Grif was leaving the army it was just a question of how. And Simmons has had Grif nearly forcibly ripped away from him multiple times, at least this way it's on Simmons terms and he knows that Grif will be okay.
I think Simmons planned this out so much that he had already accepted that Grif was going to be gone and wasn't prepared for Grif to ask him to come along.
I think Simmons stays because he already made his choice along time ago before Grif ever had a say.
