According to Dunbar (2010), The maximum number of relationships that any person can have at one time is 150. It doesn't matter how many friends we have on Facebook. It has also been found that this is the average size of our hunter-gatherer ancestor communities (Dunbar 1993). It takes far to much cognitive effort and time to maintain relationships with more than 150 people. When a relationship isn't invested in it diminishes over time. Within this number there are sub-levels, I can't remember what all of these are but the innermost circle numbers ten people, and these are the people you can really trust and rely on. These are your true friends. The definition of friend has changed over time.
This number excludes family, as family relationships are unique. You don't need to invest much time or effort into maintaining these. You can abuse family relationships and still be able to rely on family members.