By Christine Koh, CNN

(CNN) -- When a friendship hits a stumbling block, how do you know whether to work on the relationship or let it go?

It can be tempting to let a friendship fade instead of facing conflict -- especially when life feels overwhelming in other ways -- because conflict is hard. But we are already facing a loneliness epidemic, and relationship repair carries further urgency in the face of biological evidence.

"It actually is a matter of life and death," wrote Lydia Denworth in her book, "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond." "It is carried in our DNA, in how we're wired. And that means friendship is not a choice or a luxury; it's a necessity that is critical to our ability to succeed and thrive."

If you've lost touch with good friends or drifted apart in the past year, it could be time to work through hurt feelings and misunderstandings. Think of this work as a form of relationship and self-care, because being stuck in conflict saps valuable energy.

Here are five ways to repair a friendship -- or leave it behind if it's toxic.

1. Reflect and write down the good

Before you face a difficult conversation with a friend, pause and reflect. "Think of a specific moment that this friendship has brought you joy or excitement," recommended Adam Smiley Poswolsky, author of "Friendship in the Age of Loneliness." Poswolsky suggested using that memory as inspiration to write down things you appreciate about a friend. He also encouraged sharing that list in conversation with the friend.

"Beginning the communication repair from a place of gratitude and positivity is going to make the conversation a lot more meaningful," he advised.

And no matter the outcome, the positive intention will remain. "Even if there is still tension and even if you still need to take a friendship pause, or even a long (or permanent) break from spending time together, that appreciation will go a long way to building empathy and mutual understanding," Poswolsky said.

2. Choose a different way to communicate

If repair efforts have not worked via your usual tech channels, try a different way to communicate. "People are thrilled to get mail that's not a catalog or a bill. Send more postcards, write more letters or send someone a book you think they would enjoy," Poswolsky recommended.

He also suggested a deeper letter writing approach: "Try writing letters to each other before you talk. In your letter, include why you think the relationship feels awkward -- and why you want to repair it."

This approach can help you gain empathy and improve communication skills. "You may realize your friend was going through something that you were not aware of. You'll begin the all-important practice of listening, before you even sit down to talk to each other," Poswolsky noted.

3. Give it time and try again

People differ in how they deal with conflict, so remember that you may need to give a friendship some breathing room before trying again.

Marisa Franco, a psychologist and friendship expert based in Washington, DC, noted that friendships may require time to settle back into normal post-conflict -- and that lingering uncomfortable feelings may require further attention.

"If it's still awkward, this might suggest that not everyone got to share their side and feel heard," Franco said.

Franco recommended an honest, affirming approach such as, "Hey! I have felt like things have been a bit off since we had conflict. I'd love to get things back on track since I really value your friendship. I wanted to open up the conversation to see if there's any more air we need to clear."

It's also important to remember that you can only do what you can do. "If the friend would rather not repair, then you can be proud of yourself for acting with integrity. Remember you're not in control of other people, but on your end, you did all you could," Franco said.

4. Shuffle the "friendship furniture"

One challenge in long-standing friendships is when we get stuck on the idea of how a relationship used to be. The reality is, we all change as our circumstances and priorities change.

If you have tried to fix a friendship and do not feel that things can go back to the way they were pre-conflict, Denworth suggested considering whether you can stay friends in a more casual way. "I call it shuffling the furniture in your social life," Denworth said. "Not all friendships last a lifetime, and that's OK. Evolutionary biologists have found that high-quality bonds require three things: they are long-lasting, positive and cooperative. You need all three."

5. Follow the red flags

Sometimes a friendship suffers due to a miscommunication, and sometimes the problems run much deeper.

Franco encouraged people not to let a single issue break up a friendship, which is something she sees in her practice. "Conflict is an opening to recalibrate and improve a friendship, and it conveys mutual investment. Don't give up on friendships because one issue has arisen," Franco said.

But Franco did advise being aware of red flags. "If you take a step back from the friendship and notice that it's doing more harm than good; for example, your friend isn't rooting for your success, bullies you, is inconsiderate, or you feel drained or misunderstood by them ... it might be time to end instead of mend," Franco suggested.

Evaluating the balance of harm versus good is crucial. "The science of friendship shows that ambivalent relationships are not great for our health. In other words, the good does not necessarily outweigh the bad if there's too much bad," Denworth said. "Be honest with yourself about the health of a friendship and don't stick with it just for old times' sake if it's otherwise hurting you."

When life feels hard, approaching awkward or painful conversations often falls to the bottom of our to-do lists. But human connection is crucial; it's time to embrace the awkward, be honest, listen and dive in.