Believe this : she's got that beef in her right now and the last thing she's doing is thinking about you or your family unit. She's been running around behind your back for months while you're at home caring for your child, gaslighting you, and even had the audacity to flirt with the man while sitting right beside you and now you've given her all the space and privacy from you that she's been craving these past few months. Those rings around her eyes, the depleted look on her face? That's because shit just got real. She's worried the fun is over and that she'll have to find a new babysitter.
Everytime she went running, she was getting laid. Everytime she stayed late, she was getting laid. Everytime she went out for drinks, she was getting laid. Everytime she came home and ran straight to the shower, it's because she got laid and/or had his scent all over her.
There's is 0 reason for her or anyone to move out for a month if they're really concerned about saving their marriage. You don't drive a wedge between you and your partner and run away after you're caught. You've given her the green light to see if things are gonna work with her boss..
What more do you need? Do you need to walk in on her giving him a Blowjob? You come across as a good, well intentioned dude, and I'd hate for you to come back here in a month after fighting for your marriage only to tell us you got blindsided. At the very minimum, you should be taking her word with a pound of salt, showing some initiate and having a PI follow her to get some answers of your own.