How Do I know who is a real friend and who is not?

Trust is earned, never given.

They talk **** to your face and protect you behind your back.

Those who take take take but when you have a problem don't have time for you. When you go to a restaurant and they offer to pay. Some friends never will.

You will find that throughout your life, there will be few people you will have known for a long time.  The point being is maintaining a relationship is hard to do.  The point being to that is to not be overly concerned about it.  You have to learn to have confidence in yourself and not seek the approval of others.  You get confidence through education, learning and experience. So, work on that and everything else will follow.  If you will notice, there are those who are leaders because they have confidence based upon principles, not the approval of others.  Generally, a kid learns that from dad.