I wouldn't be concerned too much about her friend that you mentioned...say anything to her about it and she'll just think you're trying to control her. If it get's worse, then only you know what your tolerance is...and only you can decide if it's worth making a major change because of it.
As far as other man...you still can't control her or stop her 'if' she is doing that. WAS can justify to themselves that what they are doing is fine, regardless of the damage it does to the kids, you, and the family as a whole. 'If' that's going on, once again...only you know what you're capable of tolerating...and only you can decide if it's worth making a major change because of it.
Know this too...ALL CHEATERS LIE!
"Always go straight forward, and if you meet the devil, cut him in two and go between the pieces." - William Sturgis, clipper ship captain, 1830's.