Lotus! What a beautiful letter! I feel I've written two similar letters in my life... one I read to my ex-husband while he was in rehab and he other one I wrote to my current boyfriend and which I didn't send because I knew I wasn't ready to end the relationship.
Your letter is more beautiful than both of mine. I agree with the others. You need to be sure about your plan before you send it.
Hugs! I can feel your sadness.