I'm so sorry to hear that you are are in this position. Please listen to and take the wonderful advice that people have given you ... they know what they are talking about.
My thoughts and advice:
- Tell her to write out a full and complete timeline that includes ALL activity with any man in your marriage. This is a one time shot with no do-overs.
- Polygraph her on the truthfulness of her timeline and activities. Tell her that she fails and you will file for D. It is possible that this has gone on longer than you think.
- Assume there is more to this story until proven otherwise. Right now you do not know anything for sure.
- Start doing daily exercise ... it will help your mental state.
- Find at least one trusted friend or family member to confide in. You need someone to talk to and vent to ... handling this alone is simply too difficult. I know. I did it.
- No apps on her phone other than bare minimum.
- Check app history and find out what was downloaded and when.
- Get in to a good counselor and start reading healing library.
Hang in there ... you have a long road ahead.