"People are embedded in social networks and the health and wellbeing of one person affects the health and wellbeing of others.... Human happiness is not merely the province of isolated individuals." According to a Harvard Study, our wellbeing is dependent upon our entire network of relationships. It would seem that not only the people directly around us influence our wellbeing, so does our friends' independent network of relationships.
This research which was based on a 30+ year longitudinal study of more than 12,000 people who were all part of an interconnected network, found that your odds of being happy increase by 15% if a direct connection in your social network is happy. In other words, having direct and frequent social contact with someone who has high wellbeing dramatically boosts yours chances of being happy.
But what is really interesting is even more critical is the degree to which indirect connections influence our wellbeing. The Harvard Study found a similar effect for second hand associations. So if a friend of your direct connection is happy, the odds of your friend being happy increase by 15% - and the odds of you being happy increase by 10% even if you don't know or interact with this second hand connection.
Source: Fowler, J.H., & Christakis, N.A (2008). Dynamic spread of happiness in a large social network: Longitudinal analysis over 20 years in the Framingham heart study. BMJ, 337, a2338+.