Further damage things? What, like she'll go file for divorce? She's already done that.
I think if it's sincere, from the heart, and completely honest it couldn't damage things. You're not sending it in a pursuing manner or putting pressure on her in any way.
One suggestion, I'd leave out the I love you at the end. She knows it from the content of the letter and still may not be able to hear it again.
Maybe sign it
Contritely,
H


Me 36
Husband 35
D5
S2
separated:
10/29/07-present
Served divorce papers 1/22/09
"When the world gives out beneath your feet, it is time to learn how to fly."