We've all been there, you will get through it. There is lots of information about boundaries on this forum and on the web. They are things you put in place to protect yourself and your kids, not to control anyone else.
You might set a boundary that W can't come by unannounced, that she has to let you know when she's coming, or set a schedule for when she can come over, that kind of thing.
As painful as it is, you should seriously cut off your ability to monitor. IF she wants to re-engage with you, one of the requirements is to provide full transparency, and at that point you will want access.
To look at this point is only hurting you, because you will obsess over it, your imagination will fill in gaps and make things worse than they are, and there's nothing you can do about it. It's just self-flagellation and you don't need that.
Take some action to set her up in ways you can't monitor.
Acc
Married 18, Together 20, Now Divorced M: 48, W: 50, D: 18, S: 16, D: 12 Bomb Dropped (EA, D): 7/13/11 Start Reconcile: 8/15/11 Bomb Dropped (EA, D): 5/1/2014 (Divorced) In a New Relationship: 3/2015