Oh it's quite possible to have a fluid bond with a secondary - I know of several people that do it - especially in what is generally known as polifidelitous setups where they don't all live together.
Sorry - I know that was a bit nitpicky, but I have learned that just when you imagine how things are you meet a relationship that throws it all in the air again! I love poly for that reason - there's no one "right" way to do it, and those different ways are celebrated by the community at large.
Please check out The Birdcage - an open, friendly Polyamory forum for all parts of New York State
"Listen, or your tongue will make you deaf." - Native American Proverb