I thought she could be the one; now I couldn’t even tell you her name. What I do remember is waiting to get physical with her because I liked her so much. In the past, hooking up quickly tended to turn my relationships more casual, until they died out completely. Since I wanted something serious with her, I decided to hold off a little. Then, on our fourth date, we had sex. It was a great experience — not earth-shattering, but definitely above average. 

Seconds after it was over, I thought to myself, I have no desire to see this woman ever again. She didn’t do anything wrong. Nothing embarrassing happened. It was all fun and pleasurable, yet my feelings disappeared. I had been thinking about her nonstop for three weeks, and just like that, everything was gone. 

I suspect whatever she was feeling also vanished, because I recall waiting to see if she texted me so I could officially break things off. She never did.

Speaking with friends of all genders and sexual orientations, I’ve come to learn this is a common phenomenon. To clarify, this is vastly different than people who use other people, saying the things they know their “conquests” want to hear to get them into bed. All along, they plan on never speaking to the person after sex. Those people (who, let’s be real, are usually men) are trash. 

I’m talking about well-intentioned people who hoped for something more serious, were excited about taking something to the next level, but then lost all interest afterward. 

Judy Ho, Ph.D., licensed clinical and forensic neuropsychologist and author of “Stop Self Sabotage,” says this is largely neurophysical. Sex is a complex process with many neurological networks involved, most notably, the regions associated with rewards, emotions, and pain. This helps explain why sex can drive even the most stable and level-headed among us a little nutty. 

“When we’re being stimulated in a sexual way, a host of biochemicals such as dopamine, endorphins, oxytocin, and vasopressin flood our system and alter our neurochemistry,” Ho says. 

“If the sex wasn’t all that good, we don’t get the type of dopamine spike that makes us want to repeat the experience.”

It’s our yearning for all these powerful biochemicals that drives us toward sex. “This is the ‘chase’ part of courtship,” Ho says. “We are imagining all the ways this desired person can fulfill our sexual needs and give us that much sought after dopamine boost.”

The thing is, if the sex wasn’t all that good, we don’t get the type of dopamine spike that makes us want to repeat the experience. If you wanted it to be great — and why wouldn’t you — you may be lying to yourself just a smidge because you don’t want to admit that the physical component of the relationship was why you stopped liking someone. 

And after sex, logic returns and reality sets in. 

“Before and during sex — even up to orgasm — our brain’s emotion centers are being stimulated while the executive function part of our brain actually slows in activity,” says Ho. “This explains why we can act quite emotionally and even irrationally during the pursuit of sex and until the point of orgasm.” 

Afterward, however, “other neurotransmitters that create emotional connection, intimacy, and attachment to our partner are released,” Ho says. This is great if you’re with someone you actually want to emotionally bond and take things to the next level with, but if you’re not, the aftermath is, well… awkward. You may realize the emotions you had, even if they were present for a few weeks while you were pursuing this person, weren’t the truest. 

The final reason you lose interest after sex has to do with what’s called approach and avoidance conflict. “It occurs when there is one goal or event that has both positive and negative characteristics that make the goal simultaneously appealing and unappealing,” Ho explains. “Almost every big goal in life is like this — we have no problem approaching it until it seems like it’s about to become a reality, and once it is about to, we start to think of all of the negative reasons why this goal isn’t so great after all.” 

Clearly, this could happen with a big move, a new job, or someone you like and with whom you’re about to be physical. While you maybe thought you were ready for a relationship with this person, you realize, as it becomes an actual possibility, that it might not be what you want. You’re not ready for something serious, or maybe you are, but they aren’t the right person to have that with.

Then, after you have sex, you may be confused as to why you even pursued that goal in the first place. “There’s actually been some neuroimaging research, which illustrates the human sexual response in the brain reflecting this complex interplay of approach and avoidance,” says Ho. “It can lead a person to want to disengage from their former object of affection as soon as possible.”

It seems like sometimes (because let’s not get in the habit of using this as an excuse all the time) our own brain doesn’t truly know what it wants when it comes to sex, attraction, and dating. There are simply too many biochemicals that mess with our desire for pleasure, emotions, and logic released.

Consider it a reminder that our brains can play tricks on us when it comes to sex and love, so it’s worth it to really assess our intentions, what we want, and what we can actually offer our partner before having sex.