You've done a lot of the right stuff in a short amount of time. That's a great start on the road to recovery, which is always longer than anyone thinks it should be.
How are you? Are you drinking water, eat healthfully, sleeping, moving your body?
How are you handling the images from finding them in the act? D-day alone is a big trauma. Seeing them in an act is added trauma. You're probably also filled with grief, anger, fear, and shame. Also, my bet is that your head is filled with conflicting thoughts. IOW, you need to be very kind to yourself so you can process the trauma and your feelings out of your body and get control of your thoughts.
If you need help with this work, I urge you to consider finding a good IC.
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You mention feeling inadequate. That's normal, especially after being cheated on. It's also based on misunderstanding the sitch.
Your W cheated for her own reasons and because of her own issues. She did not cheat because of issues with you or your M.
My bet is that she saw her A as something added to your M, not something taken away from you - maybe something like: you couldn't make love to her, because you were working, after all, so in her lizard brain sex with Dan was nothing. Until d-day, when I hope she woke up to the fact that something was messed up inside her.
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Before you decide between D & R, I urge you to see yourself living a good life both ways, because you really can live a good life with or without your W.
Both paths are difficult. If you are going toward what will eventually be a good place, a good place that you chose, the tough parts will be easier for you.
If you choose wholly on the basis of avoiding pain, it's really hard to move on to a life of joy.
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I know your thoughts go every which way, but do you notice a pattern that leans toward R?
If so, I reco taking the approach that it requires 3 healings: 1) you heal you; 2) she heals her; 3) together you heal/build/rebuild your M.
You can support each other's healing, but each of us is responsible for healing himself.
If so, I urge you to think in terms of your requirements for R. Make them observable - it's harder to lie with actions than with words, although words count, too.
Total NC with Dan and total honesty should be among your reqs. IC for your W with a goal of changing from cheater to good partner should be, too, IMO.
In any case, lay out your reqs for you W - if she wants R, she might have some good ideas. In the end, decide on your joint reqs, and see how she delivers. If the reqs are observable, you 'll both know how you're doing.
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Above all, know that even though life may look like it will be bleak forever, you can survive and thrive after being betrayed. You really can heal, with or without your W.