In MY opinion, since I have been married for almost 20 years and I think I can NOW give advice..... LOL
In my opinion it is more the fault of the COUPLE and not the girl that was with this man. And I say this because I don't think an outsider is as much at fault as the ones involved in the situation because often times they don't KNOW the situation..... if HE didn't tell her he was involved, this is his fault, not hers....... if he did, then shame on her for getting involved with someone who was involved, but even at that, SHE wouldn't know he was looking if he didn't go after her, right?
ON the hand of it belonging to the couple.......... women, KEEP the men happy and they won't NEED or WANT to stray...... MEN, if you aren't happy, TALK to the women, you might find out she is just as bored with things as you are, often times this is the case.... routine sometimes makes us take things for granted and we get settled into relationships and there isn't surprises or anything spontaneous about it anymore. THIS isn't that girl's fault, it is the COUPLE's fault. I don't see it being an outsiders fault NEAR as much as some people would believe. Simply because if it comes to a time when an outsider is involved, then things have already gone bad by the time that outsider was put in a situation to make such decisions and choices.
COMMUNICATION is the key and without it, relationships on ANY level are hopeless..... in my opinion.
My husband and I are so in tune with each other that we can almost tell what the other one's thinking before we know ourselves, all because we have a very open line of communication, love and trust.