I am currently in an open relationship with a wonderful woman (Caroline), who is, in turn, in an open relationship with a great guy named Chuck. While we tend to do most activities as two separate couples, the three of us get along well and often spend time together as friends.
Caroline and I started off as roommates and rent a house together. Recently Caroline has suggested having Chuck move in with us. We've all spent enough time together that I am comfortable with this idea as I think we'd co-exist well. The reason I am writing to you for advice is Caroline has a 13-year-old child from a previous relationship who believes Dad is in a monogamous relationship with Caroline. To date we have wanted to maintain this illusion of monogamy to avoid outing everyone in our small, semi-conservative community. On the occasions when we've all been around Chuck's child together, I have acted the part of Caroline's friend/roommate, and it's worked so far.
However, if we all share one house together, I think the teenager will soon put the pieces together and either have concerns or report back to Caroline's ex, which could result in us being outed and possibly a custody dispute for the child.
So I could use your advice, both as a relationship expert and as a parent. What is our best move here? Should we preemptively out ourselves to the kid and hope for the best? Try to cover things up and act like I'm just a roommate when the kid's around? I'm also considering moving out in order to get an apartment nearby so Caroline can live with Chuck in the illusion of monogamy, and then just invite her/them over (without the kid) on a regular basis.
If or when the teenager learns the truth about our three-person dynamic, what do you think is the best way to handle answering questions and explaining how our relationships work?
Three Relationships Inside A Domain
I'm a little confused about how many kids we're talking about here, whose kid is whose, and exactly what's up with Caroline's ex.
You and Caroline live together, Caroline has a 13-year-old child from a previous relationship, Caroline's child from a previous relationship believes Caroline and Dad (?) are in a monogamous relationship (even though their relationship is over?), and Chuck also has a kid and you and Caroline pretend to be a friends around Chuck's kid to avoid potentially outing yourselves as poly to the whole conservative community. So there are two kids involved here... but your question about the three of you moving in together mentions the risk of just one teenager putting the pieces together—something I couldn't do myself.
But I suppose I can answer your question without knowing how many kids are involved or what Caroline's relationship with her ex is like or the age of Chuck's kid or whether Chuck even has a kid. I would, however, like the time I spent reading, re-reading and doing sentence diagrams of the second paragraph of your question back.
Your custody concerns are real, TRIAD. Kids have been taken away from a parent just because that parent was kinky and/or poly. The more conservative the place, the greater the risk. Vengeful/hateful/horrible exes have dragged former partners into court and argued that their kinks and/or their practice of polyamory renders them unfit. The National Coalition for Sexual Freedom is a great resource for kinky/poly parents who find themselves in these sorts of custody disputes.
So the risks here are real—before moving in together and coming out to Caroline's kid as poly (but not to Chuck's kid?), think long and hard about who Caroline's ex is and carefully weigh the very real risk of a custody dispute against the reward of living together and living more openly.
As for your main question—what's the best way to explain your relationships to Caroline's kid (but not Chuck's?)—kids aren't usually the ones with problems about unconventional forms of family. So long as they're loved, listened to, clothed, fed, and warm, and so long as they live in a low-conflict home with an adult or adults who aren't abusive (of them, of each other) or abusing (drugs and/or alcohol), kids are happy. The people who wring their hands and insist kids can't handle poly parents or gay parents or kinky parents or blended families are usually just projecting their own fear, hatred, biases, and bullshit onto children.
That said, TRIAD, 13-year-old kids can be less accepting of difference than kids who are a few year younger or a few years older—thanks to the whole "desperate to fit in/desperate to avoid negative attention" thing that's much a part of puberty as pimples, unwelcome erections, and first periods. Kicking this can down the road another 24-36 months—your idea about living in an apartment nearby for the time being—might not be such a bad plan.
Kids aren't stupid and Caroline's kid could put the pieces together even if you're living nearby. Hell, Caroline's kid may have put the pieces together already—if I follow correctly, you've been living with Caroline and her kid and secretly fucking Caroline while Caroline has been openly dating Chuck. (Is that right?) So what are the odds that Caroline's kid has overheard you two discussing your relationship? Or fucking? Pretty high.
As with most parenting decisions, every choice is potentially the wrong one.
If you tell this kid that mommy is poly and then swear the kid to secrecy because you live in a conservative area, TRIAD, you didn't come out to this kid. You dragged this kid into the closet with you and put the stress of protecting that closet—keeping mommy's secret for her—on that kid's shoulders. You've also handed that kid a weapon. I got a letter not long ago from a polyamorous woman whose ex learned she had a boyfriend and a girlfriend when her kid, furious about being told, "No, you may not smoke pot in this house," outed his mother to his angry, religious, vengeful father. (This particular dad didn't sue for custody; he outed his ex as bi and poly to her very religious parents instead.)
But if you don't tell the kid...
Right now the kid thinks Caroline and Chuck are dating and you're a friend/roommate. If the kid should overhear you and Caroline discussing your relationship and/or having sex (or if this kid already has overheard either or both), the kid could worry that Caroline and Chuck will break up if Chuck finds out the truth and the kid could wind up resenting his mother and you for putting him in a position where he has to run interference for her and help you two hide the truth about your relationship from Chuck in order to avoid blowing up his mother's public relationship with Chuck.
So you're going to have to make up your own minds about what is riskier: moving in together and telling the kid something the kid might already know or waiting until the kid is a bit older to tell the kid something the kid might already know. Both choices could go wrong. Doing nothing—allowing things to continue as they are now—could also go wrong.
When you and Caroline and Chuck do decide to come out to this kid and/or Chuck's kid, TRIAD, you'll find that answering their questions is the easy part. Kids understand the whole "boyfriend/girlfriend" concept and it doesn't take long to explain that a mommy or a daddy can have more than one at a time or one of each. Beyond that, Caroline's kid is highly unlikely to wanna hear more about your three-person dynamic or exactly how your relationships work.