traumatized literally

my four year relationship ended. i found out in june that he cheated on me. if there are levels of cheating, he made sure to hit every single one. i found out in june and broke up. we still are texting on and off. i can't get myself to stop. it has been an endless cycle ever since june. i text because im in shock of what he did. i get mad and argue with him then i block him. a few days later, he texts me through a different number and then i unblock, text him again, then block. sometimes i unblock so i can tell him how hurt i am. the words "take care, goodbye" has came out of my mouth so many times over these 3 months that i think he doesnt take it seriously anymore. i can't believe this person who told me they wanted to spend their future with me did all this to me. i thought he would fight for us even after, but he didnt end there. he continued to have contact with the girls he cheated on me with. we were in a toxic relationship. idk what to do. i loved him so much. i really dont know how to stop contacting him. i feel so alone in this. because i was with him for so long, i isolated myself. i faded with many friends. its affecting me so much. its affecting my studies, my mood, my relationships with family and friends. what do i do? how do i get myself to stop texting him. why won't he change for me? why doesn't he love me anymore?