Casey and Mike Davidson always enjoyed drinking together.

The couple, both 49, met after college while working as consultants at the same firm. Romance blossomed over work happy hours, then time spent lingering over a bottle of wine on long dates.

In their mid-20s, the pair moved to Seattle and made a group of friends who were always up for a drink. Afternoons were for hiking, kayaking and sipping beers on Lake Union; evenings were for rollicking, boozy dinner parties.

But by their 30s, their drinking habits diverged. Ms. Davidson drank a bottle of wine by herself most nights, and felt increasingly uneasy about it, while Mr. Davidson settled into life as a self-described “single-beer-a-night drinker.”

“I was really defensive about my drinking,” Ms. Davidson said, adding, “I didn’t want him watching me every time I poured a third glass of wine.”

Like the Davidsons, many couples have had to grapple with the role alcohol plays in their partnership — even if neither party drinks to the point where it causes clear, consistent problems at home, or takes an obvious toll on their health. Their relationship may still receive a shock when one partner decides to cut back or quit altogether.

“It can drive a wedge between people in terms of how they socialize, how they relax and unwind, their bedroom activities,” said Ruby Warrington, the author of “Sober Curious.” “It can be really uncomfortable.”

We asked couples, and experts on substance use, how to navigate changing tolerances for drinking within a relationship.

Finding New Pathways for Connection

Ms. Davidson, who now lives in Redmond, Wash., never hit the kind of dramatic rock bottom people tend to associate with heavy drinking, but at 40 she quit for good, and now works as a sobriety coach.

She slept better and felt less anxious and foggy, but she also worried that her newfound sobriety might hurt her marriage. “It was scary for me to stop drinking, because I wondered how we would connect,” she said.

Research on alcohol and marital happiness suggests that couples who abstain and couples who drink heavily together tend to report comparable levels of relationship satisfaction.

But problems can arise when one partner drinks regularly and the other doesn’t, said Kenneth Leonard, director of the University at Buffalo’s Clinical and Research Institute on Addictions, who has studied the topic for decades. That lopsided dynamic can lead to relationship dissatisfaction and increased chances of divorce.

The reasons for that are likely to be complex, he said, though at a simple level, couples often drink to unwind and connect, and losing that may come with some cost initially. People often do not realize how ingrained alcohol is in their relationships, experts said, even if neither party has a substance use problem.

Julie Kraft, a licensed marriage and family therapist and co-author of “The Mindfulness Workbook for Addiction,” said a major upside of the “sober curious movement” and abstinence challenges like Dry January is that they offer opportunities for self-reflection.

“Am I using alcohol for stress relief?” she said. “Am I using it to feel more connected to my partner? Am I using it to avoid my partner?” One of the first things she discusses with couples looking to make changes is to brainstorm ways they might fill those spaces or needs.

The Davidsons found connection points that didn’t involve alcohol, like going to see live music on Saturday nights at a local cafe, browsing bookstores together and going to the movies.

Arthur Tindsley, 41, from Oxfordshire, England, also feared that sobriety would change his marriage. He grew up steeped in British pub culture, but in recent years, he and his wife have both looked critically at their drinking habits, going through long periods of abstinence.

Sitting down in a nice restaurant together and sharing a bottle of wine used to be one of his most cherished activities. “All of those entrenched, habitual ways that we are partners together have had to change, or are in a process of changing,” he said.

Their go-to date night now? “It’s going to sound really boring,” he said, “but we go on a walk.”

Connecting With Your ‘Why’

When working with couples in which one or both partners wants to moderate or stop drinking, Laura Heck, a licensed marriage and family therapist based in Bend, Ore., emphasizes the importance of each individual understanding their own reasons for making the change.

“Each person has to connect with their own ‘why’” Ms. Heck said, adding, “I never want one person to lean into another person’s goal and just tack it on.” She offered her own relationship as an example: Her husband stopped drinking years ago because of a heart condition. Lately, Ms. Heck has been abstaining as well, but not because of him. She simply wants to better understand the ways in which drinking has become a habit for her — and to improve her marathon times.

Experts also emphasize that partners cannot force each other to change.

“One thing we remind everyone is that their journey is their own,” said Andrea Pain, executive director of Moderation Management, a nonprofit that runs peer support groups for those who want to cut back on their drinking. “You can’t expect anyone to change what they’re doing because you’ve set this new intention for yourself.”

The Davidsons acknowledge that they are lucky. Their marriage was fundamentally sound before Ms. Davidson quit drinking, she said, and Mr. Davidson never felt threatened by her decision, nor did he attempt to derail her efforts, something which she has seen happen among her coaching clients.

The pair have found their rhythm: Mr. Davidson continues to drink in moderation, Ms. Davidson remains sober. “The way I think about it is: If I decided to become a vegetarian, that doesn’t mean Mike has to be a vegetarian too,” she said. “But he certainly wouldn’t take me to a steakhouse.”