Sooner, I wish my h had thought like you do before his affair. You come across as sweet, not a jerk.
Maybe the fact that you did not intend for w to see the letter and she had to stumble across it hurt. Since it was not actually addressed to her maybe it was not as tender as it should have been. Maybe another crack at it would work.
I, on the other hand, have made a complete turn around. I was not able to do this with a year of therapy and medication but I did learn alot in this process. Then I found Michele's book and a similar one called "How One of You Can Bring the Two of You Together" by Susan Page. With the help of these books I was finally able to take action and change myself (note the word "myself", you are the only one that you can change). My h totally responded to my behavior change. It was exactly like it was described in the books. I was astounded! I didn't actually think it would work. It definitly was the 180's that I did. I would force myself to act the opposite of what I would normally do. It didn't even take anything big (except the sex-that was big but I forced myself there too). It was a lot of little changes.
My h has moved back in and dropped the ow (after 3 years). We are having sex regularly and both enjoying it. I feel more sincere love than ever. This has surprised me because I used to think just like you, that I would never get over an affair. The road to hell and back during the past year has really toughened me up. It has matured me and taught me how to forgive and realize that everybody is human and makes mistakes. I can't say that finally having a happy marriage was worth it, but without all of this happening we would not be feeling as great as we are. I guess this proves that EVERY situation has a silver lining.
I hope my story has inspired you to keep up what you are doing and be patient.