For me, if I am going to allow myself to be in a "relationship" with someone then it needs to be free to develop to whatever level it does. There is no set "maximum" (or defined "minimum" for that matter, it is what it is). Every relationship has the potential to evolve into "co-primary" if that's where it leads - a process that, to me, evolves over time. (i.e. you don't start a relationship by defining it as co-primary, just like I didn't marry my husband the day after I met him - relationships need time and space to grow and evolve).
In terms of practical realities OUTSIDE of the house - we do maintain fictions that facilitate smooth social interaction with people that we are not OUT to (family and co-workers/clients).
For example, I am participating in a performance tomorrow. MrS, Dude, Lotus and TT are planning to attend - along with my parents.
This is what my parents know officially:
MrS and I are married (duh).
Dude lives with us.
Dude is seeing Lotus.
They are used to Dude being included in "family" functions, even though they don't know (officially) the nature of our relationship (Issue #1 - ongoing, but not new). But where does TT fit into the picture? (Issue #2 - and the more pressing question currently).
From a position of comfort - I would prefer if my parents NOT think about the fact that Dude is dating a married woman because that might make them question (out-loud) the nature of his relationship with ME. So, the easiest answer, from my perspective, would be for TT to come along as Lotus's "friend" (actually, "gay roommate" would work PERFECTLY - and explain why they live together).
BUT - I am loathe to ask a metamour (or my boyfriend's metamour, or whatever-the-hell he is) to not publicly acknowledge his OWN WIFE in front of my parents (Lotus has already met them as "Dude's Girlfriend" - without mentioning a husband). He and I discussed this yesterday. He (and everyone) understands - they are not "out" to their families either. My parents already know that I have "weird" friends and MrS and I shared an apartment with a gay male couple in college, so they are used to somewhat unconventional living-arrangements.
Since this is not an "on-going" issue (the next time that my friends, my poly network, and my family are likely to interact in the same place is in late summer...my turn to host the summer get-together.) I'm just going to leave it up to him (or him+Lotus) as to what he would prefer to do. (Not go vs. go as Lotus's "platonic friend" vs. go as himself and let the chips fall where they may...even if the "worst" happens, it's not a catastrophe - just awkward for me personally, I'll survive.).
Me: poly bi female, in an "open-but-not-looking" Vee-plus with -
MrS: hetero polyflexible male, live-in husband (22+ yrs)
Dude: hetero poly male, live-in boyfriend (3+ yrs) and MrS's best friend
Lotus: poly bi married female, "it's complicated" relationships with Dude/JaneQ/MrS (1+ years)
+ "others" = FBs, FWBs, lover-friends, platonic G/BFs, boytoys, etc.
My poly blogs here:
The Journey of JaneQSmythe
The Notebook of JaneQSmythe