Why would someone go out of their way to contact my x and tell him everything i was planning to do?

A few months ago my x contacted me and we started talking.This is the x who dumped me years ago and of course I wanted to get my revenge.After a few days of talking and actually getting to know him we hit it off and I no longer wanted to get back at him in any way. I told the only person I could trust at the moment and I told her everything I was planning to do before I had found out I was falling for my x all over again. I told her i was going to make him fall for me and make him meet me somewhere and just leave him there like he left me. But what I failed to tell her was that I was falling in love with him and this I could not let her know. I had a gut feeling to lie to her and not let her in. I stopped talking to her and I was right all along. She became so vindictive towards me. All of the sudden my x stopped talking to me. One night he said I love you I will call you in an hour next thing, I haven't heard from him. I believe this girl had something to do with it.