WHY DO I HIDE MY TRUE SELF FROM EVERYONE?

okay, was a very sensitive person. i cared for everything, and everyone. i hated seeing people hurt. i was shy and quiet. i was very weak (physically and emotionally). people made fun or me and took advantage of me (even my best friends). so i decided to change. i just woke up one morning, sick of crying and feeling sad all the time, and so i changed just like that. i grew a thicker skin, i learned to take jokes, and to be an all round more stable person. but i grew it too thick. i became an insensitive *****. i hated everyone, everything, and even myself. i hated what i had become, but i couldn't just snap out of it. it was too hard. little by little i became a bit nicer, until i got where i am today. i am nice to people i dont know that well, but to people i know well i am still a horrible *****. we argue all the time, and i still get reall upset, but no matter how hard i try i cannot cry infront of other people. it seems impossible. then i got depressed. i was like it for ages before i finally told someone. then they told other people and i am on the road to recovery. but still i feel realll sad and hopless alot of the time. i just want to know, why when i look deep down into my heart, i feel nothing. and i hate it. i want to know who i am, and what my true feelings are, and why i hide them from everyone (including myself).