I can give you a bit more perspective looking forward. I too had the misfortune of reading some of W's love letters to OM. She was very affectionate and introspective with him. W had never been that affectionate or open with me, she was always more guarded.
When we started piecing, I desperately wanted the affection I had seen her share with OM. I tried to engage her via e-mail the way he had, but I would either get no response, or one-word answers.
In staying solution focused, one thing to think about is that you may never "get" what you read H sending to OW, and to the degree that you can train yourself not to expect it you'll be better off.
It became a real issue for me for quite a while and was destructive to reconciliation -- not that I made a big deal about it with W, it just tore me up inside.
My IC had this to share: the things that we say and do when we're courting or flirting are a version of ourselves that we cannot maintain. What my W (or your H) was "selling" to OM/OW is not something they can reasonably deliver on longer term, nor do they necessarily want to. They are engaged in a fairy tale, and that fairy tale will end.
The point is, I thought I was being denied my "real W" and she was only showing that to OM. In fact it was reversed, I was getting the real W, and OM was getting a fantasy.
Hope that helps! I second everyone else's sentiment that the more you snoop, the more you will hurt. Better not to look!
Accuray
Married 18, Together 20, Now Divorced M: 48, W: 50, D: 18, S: 16, D: 12 Bomb Dropped (EA, D): 7/13/11 Start Reconcile: 8/15/11 Bomb Dropped (EA, D): 5/1/2014 (Divorced) In a New Relationship: 3/2015