When my ex-husband’s girlfriend stepped out of the bathroom wrapped in a towel, beads of water dripping from her brown hair, she ran into me, the ex-wife, dashing from the bedroom they often share with my ex-husband’s dirty clothes in my arms.

“Hi, I was just getting his — ” I said before scurrying back downstairs, where I was doing our laundry.

I can think of few moments that better capture that time in our lives: me with my ex’s pungent laundry in my arms, trying to disappear as if I were the maid to a volatile celebrity.

For two people who need a prefix of negation to refer to each other, my ex and I have had a rather porous boundary between my place and his. He and I live on separate floors of a two-family house in Brooklyn. Our 8-year-old son can run upstairs to beg his father to let him play Minecraft and run downstairs to have the Cheerios he likes with me. I dip into my ex’s apartment when a recipe calls for chia seeds, and he knocks on my door when I need help resetting the clock that is too high up for me to reach.

We have been like this for more than two years.

Technically, we are still married, although we have filed for divorce. Some of the neighbors still seem to think we are together. The kindly pharmacist always asks for updates and sends his regards. But we aren’t a couple: We no longer share a bed, no longer smooch, no longer take turns making the salad, no longer give each other halfhearted back rubs, no longer dream of trips to Italy, no longer put our arms around each other in public, no longer fight about the shades being crooked, no longer outsource our intimacy to Netflix, no longer write checks to a couples’ counselor, no longer hope to fix it.

But for a while we were still enmeshed in each other’s lives, which is why I was caught in the act of doing a wifely chore by the woman with whom he is building intimacy and trust. After that, we decided the division between our places needed some clearer boundaries.

Some things had to change, including laundry duty.

It can be difficult to imagine feelings or arrangements that you don’t have language for. For example, learning the word “schadenfreude” to name that dark feeling within yourself felt, to me, like the pleasure of tasting an entirely new cuisine. When I learned that word, I was not only relieved of the shame of that feeling — I could also laugh at myself for it.

We don’t have the right vocabulary for our relationships with our former spouses. The term “ex” is loaded. The symbol “X” itself is a crossing out, as if, by getting married and then divorced, you made a mistake that needs scratching out with a big red pen. Or maybe the X is a coming together (the meeting point of two diagonal lines) and then splitting apart. But, like many exes, we share a child: We will never fully split. Unlike many exes, we share a checking account and a household.

My ex is the source of the XY chromosomes that made our son. He makes music videos with our child (him on the piano, the boy on the drums) and takes him camping for days at a time. My ex lives upstairs from me, encourages me to date, texts me C.D.C. updates, discusses the boundaries between our apartments so he has a chance at building a loving relationship with his girlfriend (whom I like), and he texts from the grocery store to see if I need anything.

Our marriage didn’t work. But we have made the most of our separation.

When I was a child in the ’80s, divorce meant war. If children weren’t the weapons, they were the casualties. Custody battles. Friends choosing sides. Lawyers as strategists, generals. “Kramer vs. Kramer.” Waking up in a Holiday Inn to your mother’s declaration that she was divorcing your no-good father. A father denied visitation rights after the mother convinced the judge he was unfit. Children of my generation (Generation X, coincidentally) were raised on tales about the ex’s morning stench, their ineptitude in the kitchen, their refusal to cough up alimony payments.

These days, we have our mediators. We get to keep our friends. We don’t abuse our children with hate. It’s a kinder and gentler time. But we still don’t have the words. I think we can all agree that “conscious uncoupling” doesn’t exactly roll off the tongue.

Case in point: the word “amicable.” Which means, a lack of rancor and disagreement. You meet people who say their divorces are amicable. It’s like using “tolerance” when discussing diversity: Embedded in the word is a valiant effort to replace exasperation with patience so that we can put up with the other.

“Our divorce is amicable,” you hear yourself say, and you cringe. Even in your efforts to describe your friendly relationship with your ex, which is not without some discomfort, you must admit, the language of hostility is embedded in your language.

My ex’s girlfriend has moved in upstairs. Hence, I have stopped doing my ex’s laundry, and I no longer find fine strands of his silver hair coiled around my leggings. Nor do I run upstairs to pick up my work from the household printer, which lives upstairs, or grab almond butter from my ex’s pantry when I have run low, or check that our son has enough socks up there. Now that my ex has a partner, a person who must reconcile herself to this newfangled form of co-parenting, I no longer cross the threshold of their apartment uninvited. There’s much more texting.

Yes, I was talked to.

With a lot of wincing and unnecessary apologies, my ex explained that I can’t just run into their apartment willy-nilly anymore. I can be a little dense, but I’m not so far gone that I don’t understand that protecting the couple’s privacy is essential to the cultivation of their relationship. I know and regret that having the ex-wife live downstairs costs them.

Of course, there are romantic costs on both sides. This is dating when your ex-husband shares a two-family home with you: A man comes over, leans in for a first kiss, and hears your son pit-patting in the apartment above. He tries to ignore it, but he can’t help but think, “The father of her child is directly upstairs from us.” You’re looking good tonight and, though you have little control over it, your charm has made an appearance. Still, nothing kills the moment like the footfalls of an ex on the floor above.

“Can they hear us?” your date asks, panting.

“Not at all,” you answer, kissing his neck.

“I can hear them,” he whispers.

“Yes, but not the words, right? Just sounds.”

“OK,” he says. “OK.”

The next time you meet, he says let’s just be friends.

The costs also include, at times, a magnification of your loneliness. It’s evening, you’re cooking and listening to podcasts, as much for company as for stimulation. Otherwise, it’s unusually quiet in your apartment: Your ex has taken your son upstate for a few days, and there’s no one to beg you to play Minecraft. His girlfriend stayed behind, and you can hear her voice upstairs, but not her words. Chances are good that she and your ex are talking. Intimacy, you are reminded, continues without you. So does love. You’re the odd one out.

But you also get what you pay for.

Because you love your child, because being the primary parent makes sense for your family, because your ex is still as hilarious as ever, because his girlfriend is kind and fun and playful with your child, and because you choose love over hate and what works over needless suffering, you stretch your imagination, deviate from the script, resolve to better prepare future dates for the unusual situation, accept that you would have to contend with loneliness either way, honor new boundaries, and make up the guidelines as you go, even if you don’t have the words or the script.

My son asks, “Am I sleeping here tonight?”

Yes, he’s sleeping downstairs with me, but he forgot his book. The child is the only one of us who has free run of the building. He runs to your ex’s apartment where the couple is at the kitchen table, having dinner. You can hear his little voice and their mature voices respond.

The camera pulls back. The building is like the set of a play where you can see through the fourth wall. Two people are having dinner at the kitchen table on the top floor; one is below, stage left, washing the dishes. You see a child running down the stairs, a book in hand.

Jordana Jacobs is a writer in Brooklyn who is working on her first novel.

Modern Love can be reached at modernlove@nytimes.com.

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