If you can't define " co-dependent" but know it when you see it? That's what i'm seeing.
I don't understand why people bother with non-monogamy if everything has to be about keeping track of who is having more fun. It's been my observation and experience that emtional non-monogamy (as compared with physical non-monogamy such as swinging) is better suited for people who enjoy spending time with themselves, whether alone or in the company of others, as opposed to people who require constant companionship in order to not feel inadequate or alone.
tl;dr OP, learn to be your own best friend and i promise you, this problem will magically disappear.