Valentine’s Day is coming. Some couples will spend the evening devouring oysters and chocolate (heck yeah), others will plan sporty Valentine’s Day dates (gym rats deserve love too, y’all). These days, you can even enjoy the holiday when you’re single — especially if your besties are down to celebrate Galentine’s Day. If you’ve been hunting for Valentine’s Day gifts, you might’ve noticed that February 14 seems to be all about hearts. But — fun fact — what we feel when we’re in love is actually all thanks to our brains. Here’s what’s going on at every stage of your relationship.

couple hugging on bus

1. Stage One — Butterflies: That fluttery feeling in your stomach is usually a sign that you’ve found a keeper. During this phase, it’s normal to have your person on the brain, and even to struggle to stay focused when you’re apart, according to Dr. James Pawelski, Director of Education and Senior Scholar at the Positive Psychology Center at the University of Pennsylvania and his co-author of Happy Together: Using the Science of Positive Psychology to Build Love That Lasts, Suzann Pileggi Pawelski. (Oh, yeah — they’re married too.)

“That’s normal, feels good, and is something to savor,” say Dr. Pawelski and Pileggi Pawelski. “However, if months into the relationship we are still experiencing these behaviors [it] may be a warning sign that we are not in a healthy loving relationship, but perhaps more of an obsessively passionate one.”

That’s because those butterflies are part of a chemical response. Dr. Don Vaughn, who teaches neuroscience at Santa Clara University — when he’s not giving TEDx Talks on neurohacking — explains that during the early phase of a relationship, it’s common to see a drop in serotonin levels (AKA the happy neurotransmitter) and a rise in cortisol (AKA the stress hormone). Vaughn points out that studies indicate a similar reduction in serotonin levels in cases of obsessive-compulsive disorder and anxiety disorder.

“Just like there is a time course for a relationship, there is a time course for love’s chemicals,” says Dr. Vaughn. “Although passionate, the first stage of love — which lasts roughly six months — is also characterized by symptoms of anxiety and stress, likely reflecting the relationship’s uncertainty.” So the end of the butterflies stage — something we often worry signals the end of a romance — is actually a good thing.

According to Dr. Vaughn, there are plenty of other ways to feel warm and fuzzy about your person that are totally healthy. “Research has found that when you look at someone you love passionately, you experience more complex brain patterns, a higher heart rate, greater skin conductance, and increased zygomatic muscle activity (AKA smiling), than when you look at someone you love or admire as a friend or family member,” he says. Passionate love carries on into stage two, and may even last a lifetime.

On the other hand, if bae still makes your stomach flip after a year or more, it might be time to take a closer look at your relationship. (Psst — here are the signs of a toxic relationship.)

2. Stage Two — Getting Serious: So, your stomach has calmed the eff down — now what? “The second phase for a relationship continues to be characterized by passion, but now sees an increase in feelings of safety and security,” says Dr. Vaughn. He explains that your serotonin and cortisol levels “return to baseline,” or go back to how they were when you were single. “At the same time,” he says, “There is increased levels of the neurotransmitter oxytocin — ‘the love hormone’ — which may be what facilitates the long-term pair bonding that happens at this stage.”

That bonding thing? It might be why you don’t feel like going back on Tinder. “There is evidence that long-term pair bonding changes the structure of individual neurons in highly monogamous animals, and potentially humans,” says Dr. Vaughn. “For example, once a prairie vole has mated and bonded for life, the pleasure centers of their brain change sensitivity.” He explains that after these changes occur, prairie voles only get good vibes from their one-and-onlies. “Essentially, their brain creates a positive feedback loop for monogamy, and protects against straying.”

Not convinced? Here’s how to get over jealousy in a relationship.

So, between the chemical reset and your growing bond, you’ll probably feel a lot more chill during this phase. The Pawelskis say that this is a natural evolution. “In the beginning of the relationship the positive emotions we may feel are more high-arousal ones,” they explain. Later on, though, these feelings are replaced by “calmer positive emotions of serenity, gratitude, and inspiration.”

3. Stage Three — Happily Ever After, Sort Of: “Couples [should] realize that ‘happily ever after’ doesn’t happen,” say Dr. Pawelski and Pileggi Pawelski. Staying happy requires work, they explain. “We use the analogy of a ‘relationship gym’ in our book. In other aspects of our lives, say physical fitness, we don’t buy a membership to the gym and think that by just working out once we’ll have fitter and more flexible bodies.”

As in your exercise regime, you need to keep an eye out for plateaus in your relationship. When these occur, think about small changes to push things to the next level. The Pawelskis point out that you shouldn’t try to force happiness. “Research shows that people who are happy tend to ‘prioritize happiness,'” they say. “So couples should focus on shared interests and activities (e.g., hiking together, doing the NYT crossword) that bring them happiness and then schedule them into their day.”

And the good news is, there’s still lots of positive stuff going on in the brain to keep your relationship strong. “Oxytocin likely continues to be high during this phase,” says Dr. Vaughn. But, “activity in the highly rewarding dopaminergic system — the same areas activated in sex, food, and drugs of abuse — decreases.”

Vaughn refers to this stage as “compassionate love” and notes that it’s marked by a dip in passion. However, he says, “Not all couples enter phase three; rather, many claim to remain deeply passionate for each other.”

Whether your relationship goes through two, three, or more phases, the important thing is that you nurture that bond.

Would you rather grow old with your best friend or keep the passion alive? Let us know @BritandCo!

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