I hope I can add to the discussion by putting a slightly different spin on this.
There is no universal "right" - there is only right for you and right for your partners. For some people one person is all the ever need, both sexually and emotionally, for others it's not. That doesn't make any one point of view right or wrong. So I don't think that the concept is flawed form the start at all - what is flawed is to expect ones partner to be exactly the same as you when it comes to desire or pleasure. If you are the same, then that's great.
If you have a need to have multiple sexual partners in your life, and that is part of your bottom-line - it's non-negotiable, then her needing you to only have sex with her and that being her bottom-line means that the two of you are basically incompatible and should stop wasting time beating yourselves up over it.
They say you should never enter into a relationship (or stay in one) where you are expecting your partner to change to make you happy, especially if that change is something that is fundamental to their make-up and desires. It sounds like she is expecting you to be sexually monogamous with her, and that you are expecting her to let you be with other people.
So, I think the first thing to do is for the two of you to sit down and work out whether these standpoints really are non-negotiable "bottom-lines" for you or not. If there is room for change, then work on it together. If there is not, recognize it, and go your separate ways.
(Edit to add: I have a real problem with the concept of "completing oneself" - if you see relationships as adding something to who you are, and people not being "enough" to "complete" you, then I think you are always going to be on a very rocky path.)
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Last edited by CielDuMatin; 02-01-2010 at 02:50 PM.