Amazing Grace question...SPOILERS !

Can someone please explain to me what happened at the end of this episode?
It definitely seemed that Margaret made her peace with Neil - but what was the letter supposed to be for? Why did she give him back her wedding ring. She didn't leave with "Teddy," and he just kind of disappeared. When David told him he shouldn't show his face around there anymore did he just return to the city without her? And what about her just walking away in the end when she was so sick? Was that supposed to be symbolic of her death...or was she running away again? And why did Miss Alice just let her go? Please HELP! :) Thank you.