You should calmy ask her about her contact with him and see if she replies honesty about it or denies it. If she denies it then mention to her that you have seen the phone bill and ask what it means.

That's what I think you should do,

I called my H at work hysterical asking if he was leaving me for the person he was calling on the phone, not as much what you should do...

Me~34
H~38
D6.5

EA/PA-DEC.07

Moved out~Apr.13,08
Sep. Papers~Dec.7,08
No contact order ~Dec.9,08 and again October 13, 2009