I would recommend against a letter like that, it is pursuiting and "begging". Also although Picses would love a letter like that she is in the same boat as we are....LBS. I would really get an opinion from a couple WAW. Remember talk /words are cheap....actions is where things get done. If she brings up these in things in an R talk then slip it in there as validation (the understand part....not the making it up to you part).
I think your best bet is to be a great Dad to your children (which should come easy) and a good friend to your W.
TwinDad Me 39, W 36, M 11 W - MLC, WAW???? 2 Kids B/G 3 YRS Old Start of the Long and Bumpy Road..... On the verge of piecing.....a new beginning