triple agent 

Someone who you think is your friend, but then betrays you for the sole purpose of capturing your other friend who is a double agent.

Oblivious Motherfucker: How could you betray me?
Triple Agent: I only betrayed you so you could uncover the truth about Nina!
Oblivious Motherfucker: But Jack is my best friend! You are nothing to me now!
Triple Agent: Actually I'm all that you've got.

triple agent by TheWhiteBowser October 3, 2016