I pick option #3. I just don't know; I only know what I know about myself in these situations.

Disagree. I've been there for my friends who have been completely blindsighted. In other occasion, the girl learned about cheating from the other woman. In other occasion, the guy had said he was with a guy friend, but failed to confirm the alibi with the said friend. Classics, really. But these girls really didn't have a clue, we'd see regularly, several times a week, at the time, and they would  tell me just about everything about their relationships.

Also, about 5 months into our long distance relationship - of which we'd spent together only about 6 weeks - , my Ex confessed he'd followed some girl to her apartment and pulled back at the last moment. In retrospective, I understand this was passiveagressive and manipulative, and something he'd learned from his ex-girlfriends (they were together for four years from the time they were 17 to the time they were 21, they never had sex, she never had sex with anyone before The Ex broke up with her, but made out with several other guys, including her much older and married boss). He wanted to make me jelouse. Well, I didn't reacted as he wanted, but must say I hadn't had a clue, and was hurt deep. 5 years later, when he had "an emotional affair" (well, just friendship, if you ask from him) with his now wife, I had my suspicions maybe two months before, but never thought it would go where it went.

I have to say that we all were in out early 20's, though, when this happened, maybe we'd know now, as grown women.

My current BF, didn't know his ex's were? He had to figure it out, afterwards. I guess, if you don't tell them they don't know its happening. For them, love is blind.

I believe in the "woman's intuition", if you are truly curious, you will find out.

This happened to me, my BF at the time was in love with a young lady at work - everybody knew/saw except me!

I was blind as a thousand bats!

I found out one day when I went to his office to use the phone and found an open note on his desk right next to it, impossible not to see and I wasn't looking for anything at all. It was weird.

Now when I think of this it makes me laugh! Sheesh, what an idiot I was.

So, if I hadn't lived it I'd answer perhaps women know unconsciously, but to be that blind...jeez, unbelievable. (Ahhh, Venus square Neptune...)

I was younger (and naive, still am). The next guy I was with cheated on me too - even his family had met and welcomed his new girlfriend. Me? still blind! Found out later.

I hope I've improved, but...

I think men have more self-confidence than women, so don't doubt about their power. Also women don't tradtionally jump on every guy they see, like some guys with women. So men might feel safer about being cheated on and don't project as much.