I've met some couples who were successfully open. It takes a certain type. I've come to the conclusion that I myself am reasonably well-suited for non-monogamy. I'd hoped that my woman would grow secure enough in our relationship for us to re-open it but I suspect this will not be the case.
It's not like our sex life is inadequate in any way. A lot of people would kill for it. So the notion of breaking up over this seems ridiculous at best, but at the same time I feel like it has the potential to eat at me.