I can't stand either of them but, I'd say the blame is squarely in Bear's court. He gave Chloe the green light all the way, made out his relationship was nothing, etc. Yes, she sort of knew, perhaps he may or may not have been telling the truth, but she can only go on what he was saying to her ultimately, because she was attracted to him.
You could have a gorgeous, butt-naked Angelina Jolie served up for you on a table but, if you are in a serious relationship or married, a decent guy would walk away (painful as the temptation may be!) because he values his relationship. The 'other woman' is single. She's not doing anything wrong.
Yes, you could question her decency for going after a man who is already involved (I wouldn't go anywhere near them if this was the case, personally) but she is single, and if he is putting it out there that so is he, then he is the one who is fundamentally wrong. Women who are involved with men like this consistently blame the sisterhood to a greater degree rather than hold the man accountable, but the fact is, if his object of attraction doesn't put out, he'll go and find it elsewhere anyway, because that's who he is by nature. Ditto if it's a woman cheating on her boyfriend. Nobody deserves to be cheated on.