should i or shouldnt i ??

[Mous]

I would honestly say, write the letter, just don't send her anything.
Opening old wounds doesn't always help, and she may not even read your letter.
Not trying to be a downer, but that's just how things like this tend to go.
I would say write a letter that will never be sent, and then
spend your time focusing on your new woman, and trying to do the things with
her that you never did/could with the other, or maybe you*did* do, just she didn't appreciate them.