Friends are precious, but they can also come and go, depending on how we treat them. If you want to keep them, make sure you never do any of the following things to them.
Steal their boyfriend/girlfriend. This is surefire way of proving that you cannot be trusted. Do this, and chances are this friend will become an ex-friend. While your friend is involved with someone, they are simply no-go territory.
Compete with them. Competition is natural between people, but if you take it seriously and lord it over someone, because you got 10 percent more than they did in the test, prepare for this friend's departure. Friendship should make us feel safe, not as if we are constantly in a battle for the first place.
Borrow anything without asking. From a pencil, to clothing, to computer games – always ask. It shows respect for the other person and their belongings. If you have no respect for someone's things, you also show that you have no respect for them.
Criticise their parents. Every teenager is allowed to moan and groan about their own parents, but not someone else's. If you start saying nasty things about someone's parents, they will start to avoid you.
Laugh at their clothes/home/bedroom. All people are sensitive and if you make fun of someone, they are going to feel hurt and avoid you in the future. It's fine to laugh with someone, but not at them.
Repeat something confidential. They tell you their brother's in rehab, or they kissed someone at a party on the weekend, and next minute the whole school's talking about it. If you are the only person they told, they will know whom to cross off their Christmas lists.
Drop them at the last minute. This is a killer. If someone has planned a weekend away or a day trip into the city and you agreed to join them, you cannot chicken out at the last minute, unless you are really ill or there is some really big family crisis.
Bear grudges. Everyone does silly things every now and then. Don't write someone off because of one error of judgement. Also, don't constantly remind them of it. But if someone betrays your trust in a major way or lets you down terribly, get out before you get hurt even more.
Talking about them behind their backs. If you say horrible things about someone behind their backs, they will find out about it. It always gets back to them. Don't join in when others are saying nasty things about your friend. That is simply disloyal.
Being unprepared to share. Not everyone has equal amounts of everything. While each person should paddle their own canoe, it is a kind thing to do to share things like lunchtime sandwiches, if your friend left hers at home. Share, by all means, but don't allow yourself to be used