I have never brought a girl into a relationship of mine with a guy so i do not have any opinions on that subject...
i do have a close friend that has been with his girl for about 9 years and they have an open relationship and they are very honest with each other, they are best friends. If the husband happens to kiss some girl at a club he runs home to tell his wife. His wife is not bisexual and they are both deeply in love. His sex drive is much more then her sex drive and she doesn't think that she should regulate him and has no problem with this open relationship. He never has to lie to her or be sneaky. I respect that.
My whole life i didn't believe in any other kinds of relationships other then Monogomous ones... i did not believe in dating or one night stands and I have had probably every guy cheat on me. I even had bf's try to screw my gf's while i was dating them. (like my gf's are not going to tell me)
Girls know when their man is fucking around whether they say something to him or not, they know.
Being cheated on is not what hurts for me, I think being lied to when you thought this person was your best friend is what hurts.
