Yes, this is interesting. It may mean that he is not OM, or it may mean that he is OM in her mind, but he doesn't want that responsibility and is letting her know that he is not her escape hatch.
I agree with 25 that the letter doesn't change anything. It is sad that she says she doesn't love you. But no one is guaranteed happiness in life. Marriage doesn't promise happiness. As I recall, the phrase is love, honor and cherish. I assume you are doing all that. The idea that we will be happy all our lives is a myth that brings unhappiness to a great many people. 25 is exactly right on what love is. Love is a verb, it involves doing loving acts. If you doing loving acts for someone, then loving feelings do follow.
You don't have to move because she is unhappy. You don't have to divorce because she is unhappy. The ball is still in her court.
