I agree with Anna Mu, I hope you picked it up from the trash.
While wife determines the value for her, you choose the value for you. You make the choice to do with it as it suits you. You may indeed determine it has it's rightful place where wife put it. You may not know right now. Let time decide.
Being loved is a gift, regardless of outcome. A written reminder while painful, is a treasure. Your letter remains so regardless of the value W has given it.
Mu, I have kept every card and letter I have ever received from the men who I have loved and loved me. I don't read the ones from Mr Ex or Mr M. I do however I keep them in a special place, knowing that when I am old and grey and considering my last breaths, these momemtos will be as special as they were when they were given. Time always changes perspective and heals wounds, especially at the latter end of life, when we finally see what is important.
One day Mu, I might just write you a love letter myself, because Mu you mean alot to me and a number of other posters here and you just have to know that. Biggest hug Mu.