Abnormal behavior observed.

I started behaving abnormally since 2 years. Someone's acts are affecting me a lot. I do overthinking regarding that person. When something happens which I don't like or when I feel I am being ignored I tend to hurt myself very badly. Am not able to understand things in the way they are. I always want to seek attention from that person if he fails to give I go very rouge by hurting myself Unknowingly. I always want that person beside me or else my thinking will go beyond expectations. I feel very possessive sometimes. I have gone through many things that hurt me from childhood. My parents always fight. I never had good environment from childhood. I was raised in a boarding school. One person gave me intense love where I am not able to live without him now. Being far away from him for a week will make me mad and think negative and makes me to hurt myself badly.! I would like to know the solution for this problem.. Am under severe depression. Want to get rid of this and live happily.