Meryl came to the conclusion that he had done too much to fit into any group without doing a big thing. I don't think he truly thought he was on a suicide mission, too much thought involved as he lured the walkers in and waited for the firing to start in order to cover his own shooting. I think he fully hoped and planned on taking out the Gov'. But did not expect the sudden blocked shot.
Michonne is fully committed to Rick's party as it was evident as soon as Meryl took her...all she did was to try and talk him into accepting that Rick's group would accept him as they had accepted her...she could have walked away but she returned. She is a good judge of character and even though there were times when Rick did not treat her with respect, she knew Rick and the party and that they were the ones who still had some humanity.
We saw the Gov for what he definitely was last night. Shooting Meryl so that he would turn was not humane, Rick and his group have never let someone turn and walked away from them, they ended it....always humane. There is the glaring contrast between those two.
And Andrea is the stereotype that is not archaic...it still goes on today in shows. Time and time again we see the "struggle" of the heroine time and time again rising up to only be brought back down. Only to have an ultimate victory in the end. Even with Lucy at the end of every episode she had victory. Andrea is still strapped to a chair