(((Awoken))) Sorry I've been absent when all this was going on!
It doesn't really change anything, does it? You're ready to be done with it. Just figure out how to get her out of the house as soon as possible. You thought all along this was what was happening and didn't really care. Detail shouldn't make a difference. (I know, easy for me to talk.)
Please don't call her parents! They will be supportive of her, no matter what. No matter what she's doing - she is their daughter and they WILL support her.
It must be hard thinking about your kids being there with the OM - especially if they spend time together. Seems like there should be a way to set a boundary about this?
Be strong. Just keep thinking about yourself and making YOUR life better for you and your kids.