The party-going partner now prefers chamomile tea on the couch. The lover of wanderlust has started to cling to routine. The big spender has become a frugal budgeter. Blond turns brown, turns gray, turns bald. Waistlines expand and contract. So do sex drives.

We don’t marry one person as much as we marry one version of a person, a snapshot of who we (and our partner) are individually and to one another at the moment when we say “I do.” Who we are five, 10 or 40 years later is anybody’s guess.

People change. As a result, relationships change, too.

“Not only do relationships change with time, but people change, which can affect the relationship dynamics as well,” said Michelle Chalfant, a therapist in Charlotte, N.C.

Personalities are more malleable than we may think. Most of us change, though often gradually, according to a study published in 2018 by the University of Houston, University of Tübingen and University of Illinois at Urbana-Champaign, which assessed the personality traits of 1,795 people in the U.S. in adolescence and then 50 years later. Many participants, the study showed, tended to become more emotionally stable, conscientious and agreeable over time.

But the pandemic and the disruption it brought have resulted in a period of far more rapid, intense and often negative change for many people the world over.

“The pandemic has turned the world upside down,” said Jeff Gardere, a psychologist in Manhattan and an adviser for Ro Mind, a digital health service addressing anxiety and depression. “We are still traumatized and many of us are dealing with a subsequent mental health challenge because of it.”

Dr. Gardere said that, nationwide, about four in 10 adults reported symptoms of anxiety or depressive disorder since the start of the pandemic. “It stands to reason that the anxieties and the difficulties we had as individuals and in our marriages have been exacerbated by the incredible and enormous stress of the pandemic,” he said.

“Communication has and will always be the key to mitigate negative feelings around change in your relationship,” Dr. Gardere said. “Talk about the change you experience, perceive and are impacted by. These continuous conversations should always be framed in the mind-set of learning, compromise and conflict resolution.”

The changes that the pandemic brought Treva Scharf, 58, an independent life and dating coach, and her husband of seven years, Robby Scharf, 64, an entertainment executive in Los Angeles, couldn’t have been more abrupt or sweeping. In the last two years, the couple, who live in Beverly Hills, Calif., lost three of their four parents, while Ms. Scharf has simultaneously struggled through menopause.

As a result, Ms. Scharf said she became “so fragile and needy,” adding, “I feared I was being a burden on Robby” to the point that she “worried his compassion tank would run out, or he’d lose patience with me and want to leave.”

Ms. Scharf said that “facing our difficulties head-on” with the help of therapy and leaning on friends to offset some of the support she sought from her husband, has been integral to her and Mr. Scharf’s ability to accept the internal and external changes in their life. Doing so, she added, “not only gave me new respect for him, it showed me what I was made of, too.”

The Scharfs are far from the only couple for whom recent years have been a crucible. Jenna Hewson, 34, a marketing and communications specialist for a law firm, and Christopher Hewson, 34, an engineer for a company that specializes in hydraulic fracking and reservoir simulation, had been married for five years when the pandemic hit. The couple, who live in Calgary, Canada, went from enjoying separate work lives outside of the home and expecting a second child to working from home together while parenting their 3-year-old. Then came the loss of their baby, who was stillborn.

The ensuing grief, Ms. Hewson said, left her and her husband “both so broken and hurt.”

“We had nothing to give,” she said. “There have been times following our loss where separating seemed like the easier route.”

The Hewsons learned how to be more patient with each other with the help of a therapist that they saw together and then separately, as well as nightly check-ins after their son went to sleep, which helped them remember that they are on the same team, not opposing ones. “Understanding and appreciating how your partner manages upheaval is half the battle,” Ms. Hewson said. “Knowing what to expect from your partner can alleviate a lot of confusion, disappointment and resentment.”

Loren Raye, 35, and her husband of four years, Matt Bosso, 40, who live in Bridgewater, N.J., with their 3-year-old daughter, experienced a different kind of loss in the pandemic that put a strain on their relationship. Ms. Raye, who was a radio host for the TJ Show on 103.3 AMP Radio in Boston, was let go from her job and could no longer be the family’s breadwinner. (Her husband, who works as a music curator for iHeartMedia in Manhattan, earns less than she used to make).

“I resented suddenly being forced to be a stay-at-home mom and I got very depressed,” Ms. Raye said. “The last almost two years have been emotionally challenging for our family as I have been struggling to accept, find, understand what my next step is.”

Accepting these changes and the person Ms. Raye became as a result has involved therapy as well as the couple learning to communicate better, she said. “We’ve learned how to address heavy things in productive ways during our relationship,” said Ms. Raye, who added she has also learned to accept that marriage is “never 50/50. Sometimes someone carries the other person more and that it’ll inevitably flip later on,” she said.

Pandemic or not, “All relationships go through distinct phases over time,” said Terri Cole, a psychotherapist in Manhattan. The first, she said, is the “hormone-driven honeymoon phase,” where everything is euphoric. Then, in the second phase, reality settles in and you start noticing things that bother you about the other person.

The third phase is the “make-it-or-break-it” phase, where partners begin to understand that a good relationship requires work and a willingness to “grow in the same direction.”

It was in the make-it-or-break-it phase when Diane Reynolds, 78, a retired congressional liaison for the Board of Veterans Appeals, and Dennis Reynolds, 78, a retired marketing executive and Vietnam veteran, decided to end their marriage.

The two, who live in Las Vegas, met in junior high school, married right after high school, had two sons and then divorced four years later. Their marriage collapsed because Mr. Reynolds was trying to balance both work and community college. Ms. Reynolds felt lonely and both lacked the ability to communicate.

After they divorced, Mr. Reynolds was deployed to Vietnam and the two remained distant through the years, not argumentative, but certainly not friends by any means.

Mr. Reynolds said he spent the following decades learning more about what was important in life, the need to respect a spouse and their opinions and “the value of trusting and strength of a loving relationship,” he said. Ms. Reynolds said she learned how to stick up for herself over the years, which helped her to better express her feelings.

Sometimes change is precisely what the love doctor ordered in order for two people to realize they are right for one another.

On Nov. 11, 2021, which would have been their 60th wedding anniversary, they remarried with a fuller understanding of the person each had first fallen in love with. “We are fortunate to both be forgiving people, letting each other vent, and taking a distance when needed,” Ms. Reynolds said.

Upon remarrying, the Reynoldses reached what Ms. Cole said is the final phase of a relationship, secure attachment. “Years of effort yield a safe, satisfying, enduring connection that can last for decades or for the rest of your life,” Ms. Cole said.

To those who wonder if there is any change that could be too drastic to accept, Ms. Chalfant recommends asking: “What am I OK with?”

“If it feels too much or is overwhelming, have a conversation with someone you trust about it,” she said. “You should never go against what you deeply feel and believe.”

“But,” she continued, “if there is abuse of any kind, it’s time to leave. There is zero tolerance for abuse.”

Accepting changes that you can live with, Ms. Chalfant said, “not only leads to more self-fulfillment but can also lead to a stronger relationship.” She added, “Change brings back some of that ‘newness’ and can add new passion and interest to the relationship.”