if u ask me,...i'll just say that from experience all girls really dont like the idea of them sharing their man...even if they are players themselves, there's just this tin wit seeing ur man with any other person even if u keep claiming that u dont feel any thing for him or luv him...
concerning ur friend,.....she'll just have to take her stand and avoid seeing him even if she'll have to tell him to his face...she should put herself in the wife's position and imagine how she would feel sharing her husband with som1...and not forgetting that its really!!! a small world and wot goes around  comes around...i think its a known fact that if a man dumps a girl for u, there's every possibility that he'll certainly dump u for som1 else...afterall its not like u dint meet som1 there when u came...u chased the person away even though u dint do it physically.....if he leaves his wife for her,....he could possibly leave her 4 sm1 else somtime later...
and i also think wot could be wrong with her is mayb she doesnt have any other suitor that she can pour her emotions on..so the single 1 around with all the charm is just not allowing her see the light and know wots up/.......thats wot i think...let her move around ...have more male friends(platonic) and she'll see that concentration of emotins would be avoided cos she shares it all with evri1 not just bcos a guy is being nice...and who knows, he could only be that he knows she's alone and needs luv thats y he is showering her with it so he can get wot he wants...guys can just be unpredictable...married or single