What kind of therapy could help me?

I've been having intense emotionally issues for many years now. Sometimes they are more manageable than other times so I haven't stuck to any therapist for too long. I've been hospitalized for a short time once last year around this time and after that things seemed to get somewhat better, but it has been up and down all the time. Most of the time I am very dissociative and apathetic. But then i will have a burst of intense emotion, which I can hardly remember. I have a "girl" who is always there for me. She is like an unconditional friend who is always there when I am so down that I could end up doing something very harmful if she weren't there to take care of me. I acknowledge that she is from my mind, but she feels like a different person to me. I've had her since I was a child. They are so disordered and I get destructive and so lost that I don't even remember where I am sometimes. I'll have periods of depression and others of ecstasy, but I'm not sure if there is a patter to them or not. Most of my interactions feel unreal; with the world and people. I usually feel very detached from everything even myself and it is hard to connect with people because I am always behind a wall of fog. There was only one person who could reach me sometimes and that was good and also scary for me. I was in a relationship in which started very wonderfully but then I began to get excessively paranoid and say things like I know you want to leave me, where are you?!, I would get angry and the thoughts and fears that she had left me would consume me until she contacted me again or reassured me that she was there. She ended up breaking up with me because she couldn't take it anymore, but we are now very close friends. After a horrible depressed and up and down period that she left me, I began to stabilize. My personality completely changed one day. I am usually a sweet calm and somewhat submissive emotional person. I turned into an emotionless extremely aggressive person. I felt like the most powerful person in the world. I did many things that I couldn't even image doing now; i hurt a lot of people and friends and did it all to feed my power. This other personality is the complete opposite of who I am and when I am this person I don't remember or even know my real self. I saw my ex yesterday after several days of being so aggressive, even my roommate had commented on my extreme aggression but I didn't really notice. She was soo afraid of me. She told me she didn't know me anymore, that I wasn't the person she had known at all. That everything I said was completely conflicting with the other things I had previously said. I didn't understand. But somehow she got me back to my real self and it was so scary. The feeling was so different. She said she sees saw it when we dated too. Sometimes she wouldn't even know me. She felt like I could kill her at those instances and it frightened her so much. My intense emotions, dissociations and personality changes always come due to some reaction from others and I don't really know how to control anything. I regret a lot of things I had done in the past few weeks and now that I am back to my real self I know that I can't keep going on like this. I know this is a very long description and doesn't even start to explain everything. But my emotional life is just very disordered and I find it very difficult to do anything; I am always tired trying to deal with all of this, my perception of time is very disordered and I don't feel like this world is real most of the time. It all seems so different all the time that I don't understand anything. I just need help; if anyone could please even start to directing me to what kind of therapy or specialist could help or anything. It's destroying my energy, my family and friends and my reality.