The best revenge for this person?

Me and my ex boyfriend had been together for 3 years, and we broke up only a few weeks ago. I was absolutely distraught and cried for days on end. A few days ago i noticed him and my best friend had been texting, and i confronted her about it. She said there was nothing going n so i dropped it, but today i caught them kissing in the corridor and i went mad at her and now we are not talking. Not only is she hooking up with my ex & lied to me about liking him, i've also found out that he had been cheating on me with her for the past year. I've had enough of her, she is such a slag it's insane. Don't give me any of this 'don't stoop so low' bullsh*t. I want REVENGE. She needs to know how much she hurt me.