theres this boy im going out with, who had taken advantage of my two best friends when he went out with them,
My question to you is .. then why "go out" with him in the 1st place?
Walk away from this person. No need for revenge. It just creates bad energy for you (and your friends!). What comes around--goes around. He'll get his, eventually. Until then, spend some time with a guy that spends his time doing more than 'taking advantage' of girls. Life IS indeed too short to be wasting your time.
Best of luck!