Editor's note: Ian Kerner is a licensed marriage and family therapist, writer and contributor on the topic of relationships for CNN. He is the author of a guide for couples, “So Tell Me About the Last Time You Had Sex.”

A lot of heterosexual male clients are coming into my practice admitting they picked their partner without considering sexual attraction.

During couples therapy sessions with his partner in the room, the man will claim that he doesn’t know why he isn’t experiencing desire. Maybe it’s stress, low testosterone or feeling anxious.

But when I meet with him individually, he often tells a different story. He tells me he picked his partner without prioritizing sexual attraction.

Why would a person pick a potential life partner without feeling the spark of sexual attraction? And can these relationships survive and thrive? Can something like sexual attraction that wasn’t there in the first place be cultivated later?

I’ve talked with many men in their 30s who have told me, “When I found the woman I wanted to marry, she checked all the boxes. Except one.”

Characteristics on that list include “being my best friend,” “will make an amazing mother,” “our friends and families get along so well,” and “she really loves me.” The one box that didn’t get ticked? Sexual attraction — and often the men didn’t even list that quality to start.

I was stunned.

Sexuality is the one thing that really distinguishes a romantic relationship from a platonic one: I find that it’s one kind of “relationship glue” that helps couples stay together through hard times. That’s why I’m puzzled that so many people devalue sex in picking a partner for a long-term relationship.

“Research shows that, while physical attractiveness is usually among the most important traits people desire in a romantic partner, it doesn’t actually top the list for men or women,” said Dr. Justin Lehmiller, a research fellow at the Kinsey Institute at Indiana University, a research center dedicated to sexuality. “Traits like intelligence, humor, honesty and kindness are often at least as important, if not more.”

Some men have internalized an “either/or” view of women: those who make great wives and mothers and those who are sexually adventurous, according to Chicago-based sex therapist Dr. Elizabeth Perri.

“I’ve observed this in male patients who are out in the dating world and feel the pressure to pick someone whom they perceive as ‘wife material’ but without sexual attraction, rather than waiting to find a partner who is a better fit both emotionally and sexually,” Perri told me.

How important is sexual attraction in a relationship?

Good sex can help protect against psychological distress, including anxiety and depression, helps couples achieve a deeper connection, and improves relationship satisfaction.

“If a relationship is a meal, the sexual portion ought to be considered an integral part of it, such as the protein, instead of a frivolous part like dessert,” says Eva Dillon, a sex therapist based in New York City.

“In my experience, it’s possible for women to cultivate desire for a partner with considerable effort, but if a man does not have desire for his partner at the beginning of a relationship, he will never desire her,” Dillon told me. Why count on sexual attraction coming later when you can prioritize it in a partner and enjoy the benefits from the beginning?”

Still, lower levels of sexual attraction aren’t always a problem for couples, said sexologist Dr. Yvonne Fulbright.

“For some people, a lack of sexual attraction can lead to infidelity or divorce. For others, a lack of sexual attraction only becomes a problem when one tunes into societal expectations around sex and desire,” said Fulbright, who is an adjunct professorial lecturer in the department of sociology at American University in Washington, DC.

“A lot of pressure is being put on couples to maintain active sex lives, and hot ones at that. People have the sense that there’s a type and quality of desire that needs to be achieved, with any disinterest in such considered a problem that needs to be solved.”

Some of my therapist colleagues caution against putting too much emphasis on the importance of immediate sexual attraction.

“We have this misconception that we must be physically attracted to someone when we first meet or there is no relationship potential. That’s just not true,” said sex therapist Dr. Rachel Needle. “Attraction can grow as you get to know someone and experience increased closeness and connection.”

How to bring the spark back in a relationship

What should you do if you and your partner are running out of sexual steam? Or if you want to turn up the heat on a relationship that didn’t have any to start with?

Fulbright cautioned against giving any sweeping advice. “Only partners can figure out the best way to manage this challenge in their relationship,” she said.

“Non-monogamy may work for some, but not others. Couples need to decide how honest to be with each other, how much this matter is a dealbreaker in staying together versus not, and how much weight should be given to this issue in light of other good things they have going for them,” she added via email.

Don’t feel that all is lost if you’re in a long-term relationship. For some couples, sexual desire can grow over time if they focus on it. “It often isn’t until our 30s that we get comfortable enough to ask for what we want in bed,” Dillon said.

But I refuse to agree with anyone who thinks that married couples will stop having sex anyway so why bother prioritizing sexual attraction.

“Many couples in their 50s can explore and expand their sexuality thanks to maturity and empty nests. For couples in their 60s, 70s and beyond who are able to expand their definition of sex beyond orgasm and co-create intimacy, sex can continue to be vibrant and rich,” Dillon added via email.

And keep in mind, your sexual health is a barometer of your overall health. So if you really are experiencing an inexplicable drop in sexual interest, consider talking to your medical provider. Maybe your testosterone levels really have fallen.

Whatever the source of your lack of sexual interest, just be up-front with your partner. Honesty, as it turns out, can be a turn-on (eventually).