Welcome to the latest installment of Ms. Opinionated, in which readers have questions about the pesky day-to-day choices we all face, and I give advice about how to make ones that (hopefully) best reflect our shared commitment to feminist values—as well as advice on what to do when they don’t.

Dear Ms. Opinionated:

My partner and I are in a long-term but nonmonogamous relationship because it’s long distance for a significant part of the year. When we’re apart, we both can date and sleep with whomever we like; when we’re together, we’re monogamous, which is why I don’t call it truly “open.” Recently, with him out of the picture for a bit, I found myself really attracted to a friend and I know she’s at least very attracted to me. I just really like her and would like to date her while he’s away. However, I found out she’s never been involved in anything but a monogamous relationship before even though we’re in our late twenties, and she knows that I have a long-distance partner but not about our arrangement. How do I explain it to her in a way that doesn’t sound like I want to cheat on him and preferably do so in a way that convinces her to see what can happen between her and I? My partner knows about my attraction to the friend and is totally supportive of whatever I want to do, and even willing to tell her that we’re open, etc.

Well, before I tell you what you might not want to hear, let me congratulate you on your long-term relationship: it sounds like you and your long-term partner have a well-negotiated situation that works for you, and the open lines of communication that can allow it to keep working or be renegotiated when it stops doing so. Obviously, open communication is key to any successful partnership—poly, open, monogamous or whatever—and you’ve managed to nail that aspect, which isn’t easy. And I also want to applaud your desire to be open about your long-term relationship and its terms before getting involved with the woman you’re interested in, to allow her to choose whether getting involved makes sense for her.

But when it comes to the new woman in your life, I think you might need to prepare yourself to back off. You’re in a relationship that is situationally nonmonogamous (both physically and, it sounds like, emotionally), which means that anything you start with someone new comes not only with a third party, but a deadline. And while those deadlines make sense to you and your long-term partner, you’re effectively looking for a way to involve someone whose default relationship pattern is monogamous in a non-monogamous relationship where she is and will necessarily be secondary to your other partner and where the relationship’s expiration date is effectively set from the beginning. The question you need to ask yourself, when you frame it that way, is why she might agree to be your temporary, secondary love interest.

I mean, perhaps she is leaving the area in a few months and thus she, too, is looking for a temporary situation, though emotions are notoriously complicated things that can fuck up any game plan. Maybe she’s the type of person who sets relationship expiration dates (full disclosure: I totally do this) when she’s with partners who are obviously poorly suited for long term expectations in order to keep from getting too emotionally invested. Or she could just be looking to have a mostly-sexual fling with no long-term expectations. All of those could be reasons she’d get involved in a soon-to-expire relationship with you (or with anyone)—but, given that your understanding is that she’s “never been involved in anything but a monogamous relationship before” and is of an age that it’s probably been on the table at one point or another, it’s only reasonable to question whether those are truly likely scenarios.

Because, you see, the other reason she would agree to be the runner-up for your affections is that she, too, really likes you. And having seen this situation play itself out way too often in the past, when a long-time monogamous person agrees to an ongoing, emotionally involved, nonmonogamous relationship with a partner whose full commitments lie elsewhere because they have feelings for the partnered person, it usually ends one way: painfully.

As you know better than most, there’s a tremendous focus on the ideal of monogamous relationships in our society, even if a large number of people practice monogamy about as well as I did my violin in junior high school. And while many people, like yourself, are exploring or engaging in alternate models—and doing so successfully—there are plenty of people who are just far more comfortable, emotionally and physically, with monogamy and its patterns, and just can’t get over the jealousy or the feeling of being ranked in terms of the other person’s emotions, or just don’t know how to repattern their dating habits to a different model.

Another thing to think about is that, for your friend, you would be her first experience in a non-monogamous relationship. I’m guessing that this isn’t probably your first (or your partner’s first) non-monogamous relationship and that the other people with whom you’ve gotten involved when he was away also had at least some experience negotiating the boundaries, emotions, jealousies and constraints of nonmonogamy (or else you wouldn’t be asking me how to tell her). Just think about your own first relationship for a moment: There was some emotional messiness there, right? Some moments where you didn’t know what to feel or how to express it, where everything seemed kind of overwhelming and some little thing took on a new power to hurt you? You’re potentially setting up that situation for your friend, and putting yourself in the position of perhaps really hurting her even though you’d have been honest from the get-go about your emotional limits, because she won’t have any real experience with being on either end of that sort of limit.

Being ethical is going to be very complicated in this situation, because honesty isn’t the sole standard by which to judge whether you’re being ethical to your friend—it’s just the start. It can seem like the least sexy thing to do when you want to be making out with someone, but it’s really important to decide together whether the limits that makes sense for what you and your partner want also really make sense for her—or whether she’ll just acquiesce because she likes you and wants to be making out and doesn’t fully understand that no amount of her awesomeness will be able to change your mind about leaving your new romantic relationship aside when your partner returns. And, because she is your friend, your obligations to her emotional well-being are just greater than your obligations to a stranger in a bar or someone you meet on OK Cupid because you know her, you like her, you presumably care about her. Do you want to be her first non-monogamous relationship? And, if you do, can you promise to yourself and to her that you are really up for that challenge?

So, you have talk to her: not just about your partner and your situational nonmonogamy, but what you want, what you can really give her, what your concerns about asking her to conform to your limits are, and then give her a little time and a little space to respond to you and the situation and make up her mind. And, in the same way that you do with your partner, if you two do decide to get involved, keep checking in with her to make sure everyone is still on the same page. Emotions are complicated and unpredictable, and anyone can go into a relationship with the best intentions of not getting too attached and wind up feeling things they never expected. But the last things you want are to destroy your friendship with her (let alone draw in all your mutual friends), or to leave her feeling deeply wounded and/or rejected when your partner returns.

Have a question? Email us with “advice” in the subject line. Anonymity guaranteed. Photo credit: Kate Black, kateblack.com