I'm sorry to sound crude, but if a guy gets laid out of the deal, for 20 minutes 2x/week, he's going to be getting enough.
If she balks at transparency, then she hasn't cut off contact, and you should say "The only thing I can assume, then, is that you are either still in contact with him, or are trying to leave that door open, OR, you're not willing to do the work necessary for me to feel like I can trust you again. All three of those are unacceptable to me, for my own protection."
