Why don't they just back off?

My ex bf and I have been really close always... we've always still had feelings for eachother but oct. came and he and this one girl started going out. She hates me! Idk why but she seriously has some problems I try to be nice to her and Ive never been mean yet she makes fun of me when I pass by and she stares at me with her creepy eyes. She's scary looking I'm telling you, but I dont care I keep my head high and think Im always a step higher than you, you stupid little b**** (shes wayyy shorter)... Anyways my ex and I had been talking and he told me he still jad feelings for me and we somehow got into an argument a week or two later and is now not talking to me... why? Anyways he posted on my wall mon when i liked his status that our relationship had been a mistake Im ugly and it was pretty f***ed up! And lately theyve been like talking about me and he still wont fudging talk to me! Why cant they back off?