I would say, NO, do not talk to the OW. If anyone, I would contact the current BF.
Monitor the situation right now, and confront only when you have more evidence.
If in fact it's only an EA right now, if you are moving out, and he just called her, chances are that they are going to take it to the next level.
This is what I thought in the very very beginning, that HE was having some kind of emotional affair with her, but that SHE wouldn't want anything to do with him, (I mean she was newly married, 20 years younger, 2 feet taller) really?? - NOPE, It was her all along, the first that told him - that "She was in love with him"...
Stay calm for a little while, think and observe, gather evidence.