Yup you will be worried, for a while. Even if he doesn't stumble, and does everything absolutely right. It's your brains way of protecting your heart. You also shouldn't trust him right now.
Be perfectly honest with him. "I don't trust you, and I need you to validate where you say you are, and are doing what you say you are doing when you are not here." He has destroyed your trust, and it takes a long time to get it back, and the sooner he knows that the better off you are. There are folks around here that say trust but verify, I have a different spin on it. I say do not trust, and check up, snoop, verify, and do it about a zillion and one times, and each time your find nothing you will slowly rebuild the trust.
You can't control what he does and doesn't do, and you have to accept that, but if he had an A that lasted that long there is some emotional attachement, a real relationship between them, that will take some time to kill. Things to do to be sure he is staying NC, put a keylogger on any of his devices, computers, tablets, phones. Put a VAR (voice activated recorder) in his vehicle, a GPS on it, of course do this without him knowing. Look for a burner phone, this is like the second paragraph of breaking NC in the cheater handbook. Check his car for it, check his sock drawer, his work bag, his gym bag, his suit pockets, his winter coat pockets.
If you do find that he is breaking NC there have to be some real consequences for it so he knows that you will not tolerate it. Kicking him out of your bedroom is a good start.
In the meantime prepare yourself for what you will do if it happens. Knowing that it is likely. It took a half dozen tries for NC to really stick, and ultimately it took me kicking him out, to get him to go from what I thought was remorse to real remorse.
Keep reading, keep posting.
(((and strength)))