Love is so motivating because it triggers dopamine, serotonin, and oxytocin in our bodies. But these happy chemicals come in spurts, turning off after they turn on. When your levels of the happy chemicals dip, you might interpret it as a loss of love. That can turn a completely natural fluctuation in your body into a full-blown romantic crisis in your mind.
You're better off knowing why love makes those chemicals go up and down:
Love and Dopamine
Dopamine brings about that great feeling you get when you find your missing keys. It's the neurochemical that evolved for seeking and finding. Animals sniff around for food and mating opportunities, and when they find something that meets their needs, dopamine surges. But the surge is brief. Dopamine does its job by dropping after it rises, so it'll ready to alert you to the next chance to meet your needs—and so you'll be sure to pay attention.
When you find your keys, you don't expect that great dopamine feeling to last. But when you find "the one," your body may produce so much dopamine that you assume you'll soar forever. When it finally subsides, you wonder what's wrong. You might even blame "the one" for having changed.
(To be clear, I am not saying we should keep seeking new mates to keep stimulating dopamine. I'm saying we did not evolve to be on a dopamine high all the time.)
Love and Oxytocin
Oxytocin is the neurochemical that causes trust. It's released during orgasm, and in smaller amounts when you hold hands. In animals, it's released when mothers lick their babies. Oxytocin is the good feeling of a common cause, whether a political rally, a football huddle, or thieves with a plan.
Reptiles release oxytocin during sex, but mammals produce it all the time. That's why reptiles stay away from other reptiles except when mating, while mammals form long-term attachments to relatives and herds. The more oxytocin you release when you're with a person, the more attached you'll feel. More touch = more oxytocin = more trust.
But trust can also get complicated inside the human brain. You trust a person to live up to your expectations, but you may not realize how complex your expectations are. Eventually, your loved one fails to meet them, or you fail to meet theirs. In your mammalian brain, any loss of trust can be interpreted as a life-threatening emergency. When a sheep is separated from its flock, its oxytocin dips and its cortisol surges. (Cortisol generates the feeling we experience as fear, panic, or anxiety.) This works for the sheep, motivating them to re-connect with the flock before they're eaten alive. In humans, however, cortisol can turn disappointed expectations into emergencies.
Love and Serotonin
Getting respect feels good because it stimulates serotonin. In the animal world, social dominance brings more mating opportunity—and more surviving offspring. But animals don't dominate because of conscious long-term goals. They dominate because it generates serotonin, and that feels good.
You may want to believe that your own love is pure and untainted by social status. But in other people, you can easily see that status magnifies the neurochemical power of love. And once you do, maybe you can admit that the romantic attentions of a higher-status person triggers strong feelings in your own mind. If you should fall for someone who just happens to raise your status, you can't deny that it feels good.
But your brain always wants more respect to generate more serotonin. Your loved one may give you that feeling at first, by respecting you or helping you feel respected by others. But eventually your brain begins to take the respect you already have for granted. It wants more, so it can get more good feelings. That's why some people constantly make more demands on their loved ones, and why others constantly seek out higher-status partners.
We'd be better off if we understood the origins of our neurochemical impulses.
Free love is not the way of nature. Animals are surprisingly picky about who they mate with. Sex has a preliminary qualifying event in every species. Animals (except bonobos) only have sex when the female is actively fertile. Female chimpanzees, for example, only have sex every five years. The rest of the time they're pregnant or nursing, and without ovulation the males aren't interested in them. So when opportunity knocks, it's a big deal. Brains good at navigating such hurdles got passed on, and natural selection produced a brain bent on doing whatever it takes to reproduce itself.
Happy chemicals evolved because they get us to do things that promote reproduction. That doesn't make sense in our world of birth control and sustainability pressures, but in the state of nature, lots of babies died, and you had to really focus on making babies to have a few that survived. You may not care about making babies, but your brain is inherited from creatures who did. Natural selection produced a brain that rewards reproductive behavior with happy chemicals.
Love promotes reproduction, so it triggers a lot of happy chemicals. Sex, of course, is just one aspect of reproductive behavior. It's important—love motivates you to move mountains in order to be alone with that special someone. But the survivability of your offspring is what's mattered in evolution. And that depends on competing for top quality mates and building bonds of attachment. Of course, your love is above such biological banalities. But happy chemicals feel so good that your brain still looks for ways to get more. Neurochemicals do their job without words, and then we look for words to explain the crazy motivations they create in us.
Happy chemicals give us information that's hard to interpret. For example, if I watch a football game and burst with excitement when my team scores, I see that thousands of other people share my reaction. It feels like they understand me. But then why doesn't my partner understand me when thousands of others do? The answer is simple: Spectator sports trigger oxytocin (as do politics, religion, and other group activities). They generate a good feeling of trust—and although trusting a large number of people in a limited way is not the same as trusting one person in a comprehensive way, to your mammal brain, it's all the same. It generates oxytocin.
We want all the happy chemicals we can get. You expect to get some from romance, and some from other aspects of life. But no matter where you get them, the chemicals will sag after they spurt. When you know why, you can manage your behavior despite these confusing neurochemical signals.
There's good news here: Don't blame yourself, or your partner, if you're not high on happy chemicals all the time. Nothing is wrong—you're just living with the operating system that has kept mammals alive for millions of years.
Much more detail is in my books, Meet Your Happy Chemicals and I, Mammal (including a chapter on "Sex and the Status Hierarch"). My free slide presentations, It's Not Easy Being Mammal and How Your Brain Works are available on my LinkedIn page and Psychology Today bio page, in the bottom right corner under "Research Papers."