This question arises in my mind many a times when I stay here in US far apart from friends and family.
I guess Family is our support system . Family is needed to help us when we are suffering . Family is needed when we have to hide some secrets from outside world. Family is needed when we have to celebrate something. Family is needed to help us grieve . Family is needed for emotional and financial support. Though who we consider our family might be different at different stages of life; like for a child its his mother. for a kid his parents and grand parents. For a teen its his parents. If we are able to rely on our parents for all types of support during our teen age then I guess we grow up as very Strong and self confident human beings. After marriage its our spouse. Though faces in our family keep changing or adding our expectation from them never.
Friends our for fun, for our social development which can not happen in the protecting shield of family. Though for some people friends might turn into families , but that phenomenon is quite rare these days because today friends are more into competition, in the race to out do each other professionally or financially . So that warmth which I used to see between our family friends when i was a kid , I rarely see between friends these days.