I highly recommend this new podcast that comes to us from This American Life. Some friendships/relationships cause one to have high blood pressure, say the studies and the premise of this piece.
You know how on reality TV shows contestants say "I'm not here to make friends"? Odd notion, right? Well, there's a new interesting bit/study on this very topic that I'm recommending here.
Also, if you'd like to know more about the social/historical context of the word "frenemy," check this same podcast out. Apparently, the first time the word frenemy appeared was back in the 50's.
If you'd like to pursue all of the above-mentioned topics further, listen to the podcast.