Why does she care so much about my new relationship?

Ok heres the deal. Ive been split up from the mother of my child for almost 2 years now but she has never stopped calling me. She sais im her so called best friend but doesnt wanna be with me because i am disrespectful or we werent ment to be, im not her soulmate blah blah blah. She has like 50 excuses of why we shouldnt be together and there all different. I never cheated or had intentions of cheating. She slept with other men and led me to belive we were getting back together. She would tell her friends when she was ready to settle down it would be with me again. She hurt me really bad and continues to do so. I personally dont wanna befriend her any longer. Shes always lying and treating me with disrespect. Ive asked her several times to give me space, to only call me with matters concerning my son but she still calls me whenever she fells so in turn i argue with her and tell her to leave me alone. It doesnt work. I ignore her she continues to call. Ive recently went on a couple of dates with someone and told her about it. Asked her again to give me space but she still wont. I hadnt talked to her for like a week then all of the sudden she sends me a text message asking me hows my girlfriend doing, then she asks me if im serious with her. Then she sais she wants me to be happy and she loves me and always will but she was unhappy in the relationship and felt i was also. My question is if she wants me to be happy why doesnt she leave me alone. Why would she ask how my girlfriends doing when i dont have one, i just went on a couple of dates with the girl.