5 marriage mistakes couples make without realizing it — and how to avoid them

The secret to a happier, longer-lasting marriage may involve much more than chemistry and compatibility.

Recent research published in the journal Family Process found that improvements in communication and emotional safety were linked to greater relationship satisfaction.

Maintaining that connection takes effort, particularly as couples settle into routines and begin to feel as though they already know everything about each other, according to Tammy Nelson, Ph.D., a board-certified sexologist, sex therapist and integrative relationship therapist in Los Angeles.

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"Compatibility can feel different to different people at different times," she told Fox News Digital. "The relationship will go through developmental stages just like you do."

From losing curiosity to avoiding difficult conversations, Nelson shared five common mistakes that can weaken a couple’s connection — and ways to avoid them.

Losing curiosity about a partner can chip away at attraction over time, according to Nelson.

"That’s how we fall in love, when someone's curious about us," she said. "When they come along and say, 'I'm so interested in you. I'm curious about you.'"

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"We're attracted to something in the space in between us — not so much when it's sitting next to us on the couch every night, and so we tend to lose that curiosity."

While someone may feel they know everything about their partner — "what they like to eat, what they'd like to watch on TV, what they might like in bed" — those preferences can evolve over time, Nelson said.

"Don't put your partner in a box," Nelson said, urging couples to stay curious and ask questions. "Who are they becoming? What are they thinking? What do they desire? What's their vision for the future?"

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The therapist suggested that losing curiosity about a partner can sometimes make attention from someone outside the relationship particularly appealing.

"That's why we have affairs, right? Somebody comes along and they're fascinated by us," she said. "We love that. And it's why we pay a therapist, so someone will ask questions about us."

Avoiding difficult conversations — and failing to pay attention to what goes unsaid — can create problems in a relationship, Nelson cautioned.

"Pay attention to what you're not talking about and why," she advised.

When it comes to relationship problems, couples who avoid conflict may be more vulnerable than those who openly disagree.

"It's not the people who fight and communicate all the time — it's the people who aren't fighting, aren't arguing, aren't communicating," the expert said.

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Nelson encouraged couples to notice which topics make them pull back or shut down during conflict — such as money or sex — and instead make an effort to lean into those difficult discussions.

"You're probably avoiding it because you don't want to get into a conflict, which is totally legitimate, but maybe pay attention to those spaces where there could be more room for communicating," she advised.

When couples talk about sex, focusing on complaints rather than what is working can make intimacy more difficult, according to Nelson.

"The key here is not to talk about what's not working or what your partner's not doing, or why you’re not doing it more often," she said.

The "magic formula," Nelson said, is for partners to share what they like and what is working.

"The key to the universe is, you get more of what you would appreciate," she said. "If you point out how your partner is not acting the way you want, then you're in conflict, you're defensive, you feel bad about yourself. That's not going to help, it’s not very sexy."

Instead, she recommends focusing on the positive by telling a partner what they've liked about their sex life, whether it is something happening now or a meaningful experience from years ago.

"Whether you’re a new couple or you've been together forever, start with something you appreciate, and then something that you would like more of," she suggested. "Expand on what’s already working."

Another potential mistake is allowing the everyday responsibilities of life to crowd out opportunities for growth and excitement.

Nelson encouraged couples to consider whether their relationship is primarily in "maintenance mode" or "expansion mode."

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Maintenance mode involves managing the everyday responsibilities of a shared life, which Nelson said is essential.

"You know, we need to pay the bills. We need to make sure the air conditioner is working," she said. "We need maintenance in a relationship, just like you need maintenance at a job or just in life, but you also need expansion."

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Expansion mode, meanwhile, involves trying new things together and finding ways to keep the relationship exciting.

If there’s too much maintenance and not enough expansion, one or both partners could get bored and feel stuck, Nelson cautioned.

"On the other hand, if there’s too much expansion, you're going to feel like you’re always doing something new and there's no rest and maybe not enough connection," she said.

"All relationships need freedom and connection."

Couples may also miss opportunities for connection when they feel affection toward their partner but don't express it, according to Nelson.

She encouraged couples to notice the positive emotions and physical sensations they experience when thinking about their partner — and to share those feelings with each other.

"Where in your heart or in your body are you feeling the most 'juice,' the most 'aliveness,' when you think about your partner?" she asked.

Some people are more aware of these physical sensations than others, Nelson acknowledged.

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"But if you can put your hand on your heart or on your stomach or your shoulders and say, ‘you know, when I think about you, I get this warm feeling in my heart’ — that's all you have to share with your partner. And sometimes that means everything to them."

Ultimately, Nelson emphasized that avoiding these common pitfalls comes down to ongoing attention, curiosity and a willingness to keep discovering new things about each other.