there's nothing wrong with open relationships if the people that are involved are mature and "open" with their feelings. I have friends who are involved in open marriages and they are happy. They both understand that love isn't all about sex and that they need to explore sex with eachother and other people together and they haven't had any problems...It works for them.
We've all become so attached to monogamy and forget that back in the day and still to this day, there are still polygamous relationships...even in the bible, they had polygamous marriages(of course, they were mainly for creating offspring) but they were still there.
as for me, well, I've been involved in open relationships and didn't have a problem with it..of course it was me, my bf and my best friend...it would have lasted but she moved to australia..
