One thing to look into is David Schnarch's website - he has an audio download for $10 about dealing with extramarital affairs. It's a lot cheaper than therapy, and might give you some fresh ideas about what you can do with yourself in order to keep recovering from it.
The audio was meant for pros, but it also suggests that lay-people may find it useful. It's about 2 hours long.
I think that you are in a difficult situation if you accept your W's ultimatum and let that determine your actions.
While being in the now is great, any kind of A obviously has implications to other dynamics of your relationship. Often resolving those is a big part of the need to keep exploring it.
On the other hand, perhaps choosing not to explore it further for your own reasons could be an act of integrity for you.
Maybe thinking of it as 'putting everything behind you' is unrealistic. Perhaps there will always be a part of you that hates what she did. Maybe denying that only makes it loom larger.
If it does exist, that part of you exists within a much more expansive you that allows you to move forward and create a different kind of experience for you and your W now.
Perhaps you can reexamine some of your thoughts about trust and what that means for you.
M: 32 W: 29 T: 9 Years M: 4 Years I hit rock bottom: 2/11 PA admitted: 4/11 WAW: 5/11 D filed: 6/11 now: Patience, wisdom, and growth - hopefully.