Friends are the people who caring each other but not involve in the personal life and internal feelings.
relationship are people caring each other and tend to involve to their personal life.
friendship is less close than relationship.
For example: If you go out at night, someone calls you and you tell him that you are outside. they may or may not care where you are and if you are save enough but not bother to ask in details. those are friends.(not including random calls
If you go out at night, someone calls you and you tell them that you are outside, he may worry about your safety and ask detailed info about your location... this is relationship.
hope I said it clearly.