Probably going to get buried in the comments, and obviously a throw away, but I wanted to give a perspective that wasn't tainted by bad partners or unforgiving circumstances that forces people to do these things.

My partner comes from a very conservative culture. She is great in bed, caring, and just plain awesome. I am with her for 3 years now and am very happy with her. She is 32 and I am 25. Yet, while in the relationship, I discovered I am a polygamous. Participating in the swinger scene as a single male before I met her, and rationalizing early in the relationship that I did not want to miss any "opportunities for hook ups" if we break up, I continued this sort of life style until after 6 months when I wanted to get serious. Thing is... I couldn't. It was always so tempting to get back into the scene, and I wasn't strong enough. So I live a double life, knowing if she found out, she would be devastated and not understand because of our cultural differences. Also, I care about her so much and am in love, and after many counseling session to see if it was some type of addiction or just part of my sexuality (about 1.5 years), I discovered I am a polygamous in a monogamous relationship. I still love her and make love to her like she's the only woman in my life, and have calmed down a lot since I made this discovery, I still am exploring how to cope with my newfound sexuality and the love of my life who probably would be hurt beyond measure.

I have been able to find a good balance where other partners have full disclosure of my situation, but it turns out to be more of a double life than just another side of me. It's very frustrating, and am trying to somehow, one day, tell her about this without hurting her.

There will be some hurt obviously, and it is tempting to just take this to the grave with me, but the one thing I discovered about sex and cheating is this: it isn't the sex that gets people angry. Its the communication and lying. If there isn't full disclosure about even the most taboo subjects with partners, then there will be a lack of trust and respect between two people. Sex is sex, and although it may be personal, if a partner disclosed with me that they have multiple partners, like open relationships, etc. then it wouldn't bother people as much as keeping that lifestyle away from them.

I know I may sound hypocritical with this, but I am currently still exploring what may be the right thing to do in this situation.