In my experience, open relationships can be a test of your morality (in the humanist, not Christian, sense)... one that you might not pass, especially if you are living in a very conservative area. I didn't. I fell in love with a staunchly monoandrous woman, and wasn't able to communicate in time and openly enough about my other relationships. I was dishonest. (Eventually, things also became extremely aggravated by my computer game addiction, and I often think this was more important than my dishonesty in discussing other relationships.)

Eventually, the woman in question left me, and to get her back, I had to promise monogamy. I couldn't imagine life without her, and my computer game addiction had at that time axed the remaining relationships, so I decided that monogamy was a lesser evil than losing her. Or rather: less painful.

We're married now, I'm freshly a father, and I try not to think about the matter too much, but I still wonder what would have happened if I had shown more moral strength.

In short: open relationships are not for the faint at heart!