How do you know it's done? She's out of your house, living with your MIL? She could be using her mother's phone, he could be meeting her there, a million things.
She has spent every min almost with me when she is off. There is one phone in that house which is her cell. She calls when she gets off, comes str8 over, until she leaves. We split the kids 50/50, so I am 99.9% its not going on. I have done tons of investigating. I wouldnt be trying if I knew it wasnt.