Quite a few people to tell the truth. Most recent and prominent is an ex and a friend.
The first was an ex-girlfriend who pretty lied to me constantly (justified it by saying she was 'omitting', not lying), cheated on me, carried on multiple 'emotional affairs' with other guys, and stole a few grand from me, then thought that after all this and breaking up with me (twice, but taking her back was my bad), things were just going to be fine...after she hooked up with an ex the day after she dumps me and then gets a new bf about a week later.
Second was a mutual friend who was friends with my ex and I (and a friend of my current girlfriend), I was pretty close and confided in her about a lot of things mostly the problems in my relationship and my attempts to try and get a handle on things with my ex (it was before things got bad), and she took everything I confided in her and got my ex to do it (causing the cheating, emotional affairs and lying), then blamed me for everything, claiming it was my mistakes that caused my ex to do it. Tried to pull the same stuff with my current girlfriend, thankfully my girlfriend has a brain and a soul and hasn't fallen for it.
Pretty much cut off the ex without a word and look at everything that the other girl says to me or my girlfriend through the same lens; "How is she trying to screw with me now?"