Identity/feeling of emptiness/looking back

HI,
I am 19 I'm feeling quite depressed because i have no motivation for my course and have not attended my exams.
I also have a problem with my sexuality because I had a strange sexual experience when I was about 4 or 5, although I didnt during my teenage years I feel attracted to women. (only physical)
So I keep on looking back at my childhood: I had 2 elder brothers when I was born, when I was a baby my mum left my dad (kind of ran away from him). She met my step dad when I was about 18 months. When I was 4 they had a child together, my little step brother. I found that very difficult to take, I felt completely left out because they both really gave all the attention to him as if he was some god, which made me feel inadequate and envious as I was thirsty gasping for warmth.
so these feelings have been reoccuring during my childhood and they are reoccurring now.
Also when i was 5 I had a sexual experience with a girl when I visited my dad.
I often feel bitter about my life and my luck, i find it difficult to know what I need and to put it across to people, I often find myself blaming myself and others for not getting what I want.
I am extremely sensitive, I cry alot for no reasons!!
Sometimes I would like to think that my past has made me like this so that I can detach myself from it and be who I want to be and get evrything I want from life and feel a sense of integration but everytime I have a low I still feel it's all my fault, I feel like giving up. And sometimes I am envious of others and wish I could be them.
please help XXXXXXXX how can I repair myself?