The worst partners often make the best lovers. I don't mean skilled. I mean unforgettable. The kind we still think about years later, even though we know we shouldn't.
Have you ever been in a relationship society calls toxic? The kind that made you feel like a crackhead? Most people I know have, at least for a few months. And nearly everyone agrees on one thing: the sex was incredible. Those people often sit comfortably in your top three.
I used to think they did it on purpose: great in bed, deliberately, to keep us hooked. That was my theory back when I was in one.
Almost a decade later, I'm second-guessing it. Maybe some of them do it on purpose, but something else is running underneath, whether anyone is steering it or not.
Engine 1: we cannot predict them
Toxic relationships often revolve around a concept called intermittent reinforcement. I’m not crazy about clinical terms, but this one is really worth understanding.
Our brains respond more strongly to rewards we can't predict than to rewards we can. Shit, shit, joy, shit, shit hooks us harder than peace, peace, peace, joy, peace, peace. The biggest dopamine spike doesn't come from the reward itself; it comes from the gap between what we expected and what we got. Neuroscientists call it prediction error.
Think about rain. When it rains every day at 4 pm, we stop looking at the sky. We grab the umbrella and move on. When the weather is uncertain, we're at the window all day. The rain didn't change. We did.
Now replace the weather with a person. With a steady partner, we expect good sex, and we get good sex. Expected. No error. Content, modest hit.
With an unpredictable one, every night is a coin toss. Warm and present, or distracted and cold? So when they suddenly turn wildly passionate, the brain registers a massive error (wait, I did not see that coming) and floods us with dopamine.
We didn't fall for a great lover. We fell for a slot machine.
Engine 2: our body doesn't know what it is feeling
This is where it gets stranger.
A racing heart, shallow breath, sweat, that hollow feeling under the ribs. Fear does that. So does craving. The body sends the same signals for both and lets us guess which one it is. Our body trusts us way too much.
The psychologist Dolf Zillmann called it excitation transfer: arousal lingers after the stimulus ends and spills into whatever we feel next. In his studies, people who'd just pedaled an exercise bike reacted more strongly to what came after, especially once their hearts were still pounding, but their minds no longer blamed the bike.
In a toxic relationship, the fight is the bike.
Three hours of arguments or a day of silent treatment, then they suddenly pounce. Our heart is still pounding, but our mind has already forgotten it. So it reads the pounding as lust, and the caption says "incredible sexual tension."
First date nerves, fights ending in make-up sex, or relationships with unclear boundaries all stem from the body's high-energy state misinterpreted as love or passion.
Engine 3: relief is not intimacy
Two engines make us misread a night. The third one keeps us in the house.
Loop this long enough, and it becomes what's often called a trauma bond. The cycle has a shape most of us know by heart, the same one psychologist Lenore Walker mapped in abusive relationships:
Tension → Crisis → Explosive Relief (Sex) → Honeymoon → Tension again.
The sex sits at the relief stage, and that's the key. After hours of threat, touch floods us with the chemistry of calm. It's addictive not because the sex is mind-blowing, but because it feels like rescue.
So yes, that is why reconciliation sex is amazing. The fight was the foreplay.
We spent three hours convinced they would leave, and our body was ready to be abandoned. When it doesn't happen, all that tension lets go at once. Call it what it is: a hostage walking free.
This is also why breakup sex makes people second-guess their decisions.
Breakup sex combines the usual intensity with a sense of scarcity. It's the final offer; neither of us is bored or pretending. For the first time in months, we're both genuine about something. Then, lying in the dark, our body delivers an unexpected verdict: something so powerful can't be meaningless.
So we go back. Our body made the decision, based on stupid data.
Same Engine, Better Neighborhood
Here's the twist: none of this is exclusive to toxic people.
The same three engines run every new relationship. In the first months, we can't predict them (will they text back, stay the night?), our bodies buzz, we call it chemistry, and every reunion feels like relief. That's the honeymoon phase. It's the same machine in a better neighborhood.
And novelty is its own reward: a new body, new smells, sounds, angles. The brain loves a first time.
The difference comes when the engines quiet down. A healthy relationship runs out of uncertainty and hands us something steadier. A toxic one never runs out, because it manufactures the uncertainty on demand, at 10 pm on a Tuesday.
And the cheaters
Same three engines, worse intentions.
A cheater isn't always seeking better sex. Often they've found a way to restart the cycle while staying safely inside their main relationship. Novelty without moving out.
Cheating pays out from four places at once: sex, novelty, risk, and scarcity. The sneaking, the secrecy, the 1 am text. It's a slot machine, plain and simple. And every time it pays off, the brain learns to reach for it faster.
None of that excuses anyone. It just explains why a hotel room can feel more alive than a marriage, and why that feeling says nothing about which one is real.
When the engine goes quiet
If you saw yourself in every engine of this essay, that's a clue. You've probably been there. And if you've been there, there's a good chance you've also been somewhere else: with someone kind, steady, good to you, and found yourself quietly bored.
Maybe you left. Maybe you called it "no spark." Maybe you told your friends it just didn't feel right.
Here's the thing underneath the thing. That boredom you felt with the nice one? It was your body, still tuned to the slot machine, staring at a perfectly good person the way a gambler stares at a savings account.
We don't call it peace. We call it "something's missing." We break up with people for the crime of texting back.
And then we wonder, over a third glass of wine, where all the good ones went.
They're fine. They're at home. They texted back.
