The real challenge is knowing how to distinguish between being "in love" with someone and truly recognizing that they are "the one." This has to do with biology. Falling in love is a neurological state that helps you to get closer to a person by losing some of your natural fears and defenses, according to Dawn Maslar, MS, an expert in the science of love and author of Men Chase, Women Choose: The Neuroscience of Meeting, Dating, Losing Your Mind, and Finding True Love.

"You can tell you are falling in love when your serotonin level starts dropping. You become obsessed with the other person. You might not be able to eat or sleep, you just keep thinking about them," says Maslar. "Falling in love is a temporary state that changes your brain. You actually lose cognitive ability. So, some suggest that you should date for two years before you decide that they are the one."

Being in love can keep you from seeing any flaws in your partner. You believe everything about them is perfect. "This is why many people make poor long-term relationship choices," says Doares. "If you have found 'the one,' you are aware they aren't perfect, but their imperfections are not deal breakers."

"'The one' encompasses a variety of characteristics such as compatibility, chemistry, deep love, admiration, respect, fun, and humor," says Dr. Rebekah Montgomery, a clinical psychologist specializing in relationships and helping couples prepare for marriage.

"However, I think the most important quality in 'the one' is the commitment to work at it. All of the aforementioned qualities might exist when you are dating, but how do you continue to foster them years in? Finding someone who wants that and wants to work at it with you is key."

"A meaningful marker of a relationship's health is observing what it brings out in you and in your life," says Dr. Montgomery. "When we are in healthy relationships, we are often happier and healthier." If other areas of your life are flourishing, it may be a result of your relationship.

Pay attention to how you are doing at work and in your relationships with friends and family. When your romantic relationship is solid, you can feel confident exploring other aspects of your life. If your partner believes in your ability to accomplish your goals and expresses their support, you are more likely to achieve great things. "Healthy relationships have that nice balance of making us feel accepted and challenging us to grow," adds Dr. Montgomery.

As far as the question of how long you should date before determining someone is the one, Dr. Montgomery says it's less about a number of months or years, and more about the experiences you share.

"Relationships are often easy and fun in the beginning. You want to navigate challenges together and know you can come out on the other side stronger," she says. "You want to know you can be vulnerable and share the deep, scary stuff with your partner and feel closer after. Those things take time, but are more important than [the actual amount of] time."

"'The one' has all of the attributes you require in a partner and none of the 'deal breakers,'" says Doares. These attributes might include traits like intelligence, a sense of humor, attractiveness, ambition, or liking the outdoors. Deal breakers may include being physically or emotionally abusive, being condescending, selfish, disrespectful, dishonest, and so on, says Doares.

The "in love" effect can last anywhere up to 36 months, according to Doares. She explains that while you don't have to wait all this time to figure out if someone is "the one," you do have to be honest about any contrary feelings or behaviors that arise. "If you can't resolve these in a way that aligns with who you are, this isn't 'the one,'" she says.

"'The one' makes you feel loved and secure. You are able to be yourself and feel accepted. They make you want to be your best self and they bring that out in you," says Doares. "You don't feel scared of their reaction if you want to tell them something that may be hard, either to say or for them to hear. There is balance in how you interact."

When someone is truly "the one," they will make time to be with you, listen to you (even if they don’t agree), and support you. "There will be a feeling of comfort, like you fit together. You can be yourself without fear of rejection or criticism," says Doares. "No aspect of their life will be separate from you. That doesn't mean you are always together, but just that there are no secrets."

She also stresses the importance of compromise. Whether you're doing what you want or what they want, both are done with an open heart and a loving spirit. She says that if someone is "the one," they should make you feel like a priority. They will include you in their thinking and consider you when making decisions.

Sometimes, though, the only evidence you really need to know someone is "the one" is a feeling in your gut telling you just that. "Knowing if someone is the one is often about learning to hear your own inner voice and trusting your judgment," says Dr. Montgomery. "We know when something feels healthy and right."

Trust your instincts, and pay attention to how this person makes you feel. If you feel happy and healthy, you probably are. And if you enjoy spending time with this person, you know that you can be completely yourself around them, and your shared communication and problem-solving skills are strong, then they might just be "the one" for you.

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