Why do people develop "crushes" and how long do they last?

"Crush" is a colloquial or slang term for having affectionate, romantic, or desirous feelings for someone. The term is often used when talking about the affection young people feel for another person. Unfortunately, crushes may be unrequited-- that is, only one person has feelings for the other. 

People develop crushes for a variety of reasons, but all crushes have a human need in common. Humans are social creatures and we thrive in relationships. These relationships may be parental/familial, work relationships, or even friendships. As we age and our bodies develop, our hormones start signalling that it might be time to find a mate. Most humans desire a long-term, romantic relationship with a partner. While our evolutionary drive for partnership is to mate, the best matches are between people who find people emotionally and mentally attractive in addition to any physical attraction. When puberty begins and hormonal changes start signalling and interest in mating, we often begin to feel this emotional and mental attraction to other people. Of course, crushes may involve physical attraction, but this isn't always necessary.

In short, we develop crushes because our bodies and brains have evolved to want a romantic partner in life.

Crushes develop from and are sustained by positive events. For example, if there's someone you have a crush on, think about what things happened to make you like them. Are they physically attractive? Do you have a lot in common? Are they funny, or kind, or responsible? The crush may last as long as you know and spend time around this person. If you stopped spending time together, the feelings you have might fade. Alternately, the crush might fade away if you see this person doing something you don't find attractive.

Having a crush on someone can be pretty frustrating, especially if you don't know how the other person feels. You could have a friend speak to this person for you and find out if they have a crush on you, too. If your parents are okay with it and willing to accompany you, you might ask this person to go see a movie or have lunch. If you really just want this crush to be over with, try throwing yourself into your hobbies as a distraction.