How does sadism develop in a person?

so im 14 now and i love when other people suffer i remember i used to practically torture this neighbor girl when i was about 9. I also like to hurt myself. i have burns and tons of scars all over my arms and legs and its not because im "emo" i just like it the way the scars look and blood. these feelings keep getting stronger as i get older and its starting to worry me. Are these thoughts ever going to go away or is it just going to get worse... Dont bother telling me to see a therapist or whatever because my mom absolutely refuses to take me to one no matter how much i ask.