You might like to think about this in terms of the way you identify and classify the people around you - and how this classification system affects the way you behave towards them (and, of course, how they behave towards you.
as you stroll around your School or College, you come across various people:
Some (the majority) you do not know. They are identified and classified as "strangers". You do not respond to them in any way and they do not expect any response from you. In fact, if you did respond to them, they would think you were a bit odd...
Some (a reasonable number) you identify and classify as being in one of your classes. They are identified and classified as "associates". You may respond to them by saying "hello" (if you think they require a response), but its unlikely that this would be taken any further (you are unlikely, for example, to engage them in anything more than general pleasantries...).
Some (a much smaller number) you identify and classify as "friends". You would respond to them quite differently. You would stop and talk to them about all sorts of things. They would expect you to do this and would probably feel hurt and a little confused if you ignored them.
Some (perhaps one or two) you would identify and classify as "very special friends". These are people who you would not only stop and talk to, but also touch. You will talk about things with these people that you would probably not talk to anyone else about. If you did not respond appropriately to these people they would be worried about why you were acting so strangely.
When you start to look at things in this way, it should strike you how complex our relationships are (even this relatively simple form of mundane, everyday, social interaction) and how clever we are to be able to recognise different relationships and respond to them accordingly...