i disagree with your teacher. her idea regarding severe traumatic events is usually the opposite of her assumption in that people usually cannot forget them. you've been through alot, to say the very, very, very least. it's beyond the beyond. memory problems are symptomatic of many different emotional states. psychoanalysis is key for you to digest this awful experience. i'm so sorry. that you're in college and self aware enough to post on here looking for answers is a clue that you are smart, strong and insightful and self reflexive. perhaps you're college can refer you to a good analyst. nothing will get fixed here. a good analyist over a long time will change your life. it will take time and dedication and you will have to face pain and anger and many other things. be patient with yourself. you will come out on top and i bet your memory will improve.
OH YEAH YOUR BRAIN USUALY BLOCKS OUT THE GOOD AND THE BAD. THE ONLY WAY YOU CAN RECOVER FROM THAT IS TO SEE A REALLY GOD THERAPIST OVER A LONG PEROID OF TIME