How to get pure evil revenge?!?

Okay do me and my ex are going through a rough time we have been for the past 10 months he has a new girl and some mistakes were made, I tried to move on a found this one guy he seemed good and nice at first but one day he just turned on me I don't know what happened he started texting my ex saying a bunch of sh*t and that almost put us at risk! But we managed to get by it, although one thing is not one of our friends know that me and my ex still even talk let alone meet up occassionally. And I had told this new guy about our situation I said if your pissed off take it out on me not ruin my relationship with my ex! He promised that would be the end tonight he saw me and my ex together it was awkward but my ex kept saying he felt like he was watching turns out he was and taking pictures !!! Although me and my ex never did anything we did get close with eachother. I can't stand the **** and I won't let him walk all over ne. And I can't let this affect the realtionship my ex has with his new gal. So please give me some tips to make this guy beg he never had met me. I'm a girl who likes revenge when someone tries to f*ck me over.,:)