Rick was a lame pussy and apparently all it took to change him back was Michonne talking sense into him. Which also happened a couple episodes ago but he disagreed with her then. What changed? Negan waltzed in and murked Spencer, whom Rick probably want to stab his own self.
Again, massive 180 and about face with Rick as a character for the purpose of the plot. Did I like the episode? Sure... I liked that it wasn't focused on one character. I liked that they came together and did the bro hug. I liked the gun as a symbol of Rick regaining his dick, because he was clearly without one for 3 episodes.
Michonne didn't completely convince him. When Michonne came to him and said that, he had already resolved the conflict. Michonne just made it hella concrete to him and made him know that they were in it together. He had been kneeling in the cell as if he was thinking (I'm assuming the cell will be important later.) After she told him, he said "yeah, I know that now."
What changed was Rick's realization of what that guy in the Kingdom was trying to convince Carol and Morgon of (There's a reason he appears in this episode). He said something like: "We have peace with the saviors now, but you look at them wrong and things go south." Rick's fear completely resolves around losing people, not around Negan. Rick thought he could keep his family safe by abiding by the new rules. He told Michonne, "We do this and we have some kind of a life." He thought that Negan would simply leave them be for the most part, at least to the extent of not killing anymore. But he had to find out the hard way.
Rick and Aaron go through hell and hot water to get the supplies for Negan. Supplies that they need themselves, but they do it to go towards the quota that keeps them alive. Aaron nearly dies for it, only for the both of them to get home and have a Savior grunt beat Aaron nearly to death and for Spencer to have gotten gutted for "Not having guts." Which triggered Olivia's death of course.
It would have been one thing to kill carl which Negan strangely didn't do, but he killed Spencer for no good reason at all. I'm not sure why you'd think Rick wanted Spencer dead.
Negan proceeds to say "Whatever's waiting for me at the gate isn't enough" before having even seen it. Take Eugene with him, so now Rick has lost six people in total, 4 dead and 2 taken, 3 before abiding and 3 after. Whether he follows the rules or not, shit is the same and it'll never be enough. Negan will squeeze and squeeze till their's nothing left, so "You win, but you still lose." (The note is representative of the situation)
This is what changed in my opinion. That's not a 180, that's a real ass epiphany, one that Rick was too shook to see sooner. I think the show did a great job of pointing out the change in Rick's demeanor.
And damn you really like the who no dick/no balls/pussy/emasculation angle don't you. Funny because the women in this show have been the most aggressive in coping with the situation.