First, an AWFUL song quote, from Fallout Boy: "Best friends, ex friends to the end, better off as lovers and not the other way around!" That was a breakup cd for me once, and I adore it on that basis.
Honestly, RP, I handle this in a bit of an unorthodox fashion. My definition, personally, of poly is being in the relationship with every person in your life that makes the most sense for the two of you.
The biggest predictors to me of whether or not primary status is a good idea are:
- compatible life goals: I could NEVER be with someone who wouldn't want to raise my presently non-existent children, and the thought of a white picket two bedroom home in the suburbs makes me nauseous, for example.
- compatible conflict resolution styles: If you don't know how to fight when she does X or he says Y, you're going to hate each other.
- mutual interest: Obvious, but worth stating IMO.
Beyond the primary stereotype, anything goes once we're friends. If you'd make a good housemate with me, I want you in my house. If you'd make a good lover with me, I want you in my bed (and... details, details, etc.). If we could start a business that'd function and make us happy, let's do it! I have a nonsexual girlfriend and a sexual friend as a result of this policy... We have the relationship we want, how we want it. If we decide we don't want that thing anymore, we change the particulars.