It sounds like you are looking for a unicorn. Try doing a tag search for "unicorns" and "secondary" see what comes up. Your idea of what poly is thee most common. A lot of couples think poly would be a great idea if only they can find a woman that will agree to commit to them as a couple and be just with them, and not only that, help out and be secondary to the primary woman in the relationship... and not date anyone else. I'm not saying that you require her to fit the bill on all these point, but just saying that this is the most common idea of what poly could be.
Thing is that it rarely happens that way. There is almost never a woman that would be interested in this situation; because it is daunting and a lot of work to understand and relate to a couple that has already solidified their relationship; because they think it is fun sexually and even feel some love for both at the same time at the beginning, but when the novelty wears off they find they love only one. The "triad" breaks into a "vee," jealousy and reigns supreme and often the secondary woman is dumped because the couple find that their primary relationship is falling apart.
I would suggest looking at what it is that makes you think you would not want to share. Find our if you like women by dating some. Find a way to maintain your own independence and then go about the task of letting go of you partner so that they might find others to find love with also... this brings it back to you tenfold usually. You also could find love and bring it back to him tenfold. If you find community to be involved with you might make some friends and who knows, you might find a love that you both could share, but by seeking it out of thin air will likely be very difficult and frustrating.
I don't mean to put a downer on it all, just giving you some facts. Really if you do some reading then you will find that there is much more to it than meets the eye... others have ideas too and some here are in triads... perhaps they will chime in with how that all got started for them.
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