It is hard to learn to trust yourself, and your feelings after Dday.
I can tell you that immediately after Dday, and he commited to R I was convinced we were going to heal, all would be right in the world again, and we would be happy. Of course about 72 hours later, he was acting angry and frustrated about silly things, seemed off. By 2 weeks he was angry anytime I would be upset, or ask questions. Yup broken NC at 72 hours or so.
Next go round same thing, took a bit longer, but felt something was off, pressed him, she contacted him, blah blah blah.
He did a burn phone, a made up email address, and of course secret meetings.
The keylogger is what ultimately saved our M. That was what finally gave me the proof, and the strength to say I was done. Luckily that was when he got his head out of his rear.
Trust your gut, don't trust him, snoop, check phones computers, tablets, all of it. when you repeatedly find nothing you will start to trust again. If he doesn't get that you need to do this, then he isn't remorseful or understand what he has done yet.