It's a bit hard for me to answer since there was always too much drama going on...
For me, the only times I have been "completely content" in any real way were when I had the right mix of partners and they were all nice to each other. By "right mix" I mean that I had someone with whom to share and express all the parts of me that were occupying me at the time.
There are times when I am not on the look out for more. Still, I end up looking most of the time, since I usually have a lot going on, and much of it I have no-one to share with. I don't think this is fundamentally poly, nor do I see it as a problem. Some people have an itch to grow and change; others don't.