Not all friendships are for life. Whether a specific incident occurs or you and your friend simply drift apart, the end of any relationship can be sad. Certain types of friendships are harmful, and ending them is for the best. Grief and mourning are natural after the loss of a friend, according to Dr. Irene S. Levine, Ph.D., in the Huffington Post article "Seven Friendship Recovery Affirmations." To overcome the pain, remind yourself why the relationship ended and why you may not have been a good match. Focus on making new friends and enjoying the healthy, positive friendships you still have. Most importantly, find the lesson in the experience.

Consider the Cause

Some friendships end for distinct reasons. One friend has hurt the other. One friend moves away. One friend becomes too bossy, too busy or too critical. Other friendships simply fade away mutually over time. If both friends are willing, these issues can sometimes be repaired. Other times, friends must learn to let each other go. To overcome the loss, think carefully about why the friendship ended and why it might be for the best. Toxic friendships, for instance, are more harmful than helpful. Florence Isaacs, author of "Toxic Friends/True Friends," told CBS News that a toxic friendship is often "unsupportive, draining, unrewarding, stifling, unsatisfying and often unequal." If a friendship adds too much work and chaos to your life, it may not have been worthwhile to begin with.

Make New Friends

Making new friends can help you begin to feel better. Develop an out-with-the-old, in-with-the-new mentality. Build deeper connections with recent acquaintances, meet people online or participate in activities where you can get to know others with similar interests. Head to a community gathering such as a bookstore reading. Take a cooking class or a writing workshop. Whether you've become distanced from friends or recognized that your friendships are toxic, you're not alone in your search to make new friends, says psychologist and professor Andrea Bonior in the Huffington Post article "You're Not Alone: Needing and Making New Friends As an Adult."

Focus on Remaining Friends

The loss of one friend does not mean the loss of all friends. Don't let your sadness over a failed friendship detract from the positive relationships still functioning in your life. Arrange to get together with favorite nearby pals or friends you haven't seen lately. Focus on maintaining and nurturing these existing relationships rather than dwelling on the one you lost. Stay in touch with people through social media, meet up in person over lunch or write "this made me think of you" emails, recommends Gretchen Rubin in the article "Eight Tips for Maintaining Friendships" on Psychology Today.

Learn a Lesson

Most tough losses can help you learn a lesson. Look for a light in the situation. If you regret the loss, evaluate the friendship and think about what role you may have played in allowing it to slip away. Consider how you will avoid the same mistakes in current or future friendships. If you feel good about the decision to move on, assess what positive changes will come from letting go. For example, you might get to spend more time with friends that make you happy, or you will no longer be made to feel guilty when you don't have time to meet up with your old friend. With most endings come new beginnings, and concentrating on growth can help you have a positive outlook.