Don't ask the friend. She's likely not going to be truthful with you, and it'd only get back to your wife anyway.
To me, the UNKNOWN is always worse than the KNOWN. I didn't want to live in "suspicion" either, which is why I chose only to deal with hard facts and data points. Yes, it was hard, but it prevented me from making all sorts of strategic and tactical mistakes, and even emotionally it helped me detach (trust me, the "loving" part of "loving detachment" was much more difficult than the "detachment" part with some of the intel I saw and heard about what she was doing!).
