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.”