How do you know if someone is bad for you? What do you do?

I mean it sounds like SUCH a naive question, but sometimes the simplest-seeming questions are the hardest to answer! And sometimes it is really NOT that obvious that they ARE bad for you. I know this person who has been on my mind for so long that I don't know what to do anymore. I know there are so many perspectives to take, but don't know which one to take, or how to look at the situation. I just don't understand this person, any thought concerning him just seems unclear and superfluous and I do not know why that is. If I stop obsessing and thinking about him, I know that I can grow and move on, and then the answers will come to me when I am no longer affected by all the conflicting and confusing emotions. But I worry that if I stop thinking that I will lose some kind of control over the situation and that I'll have to live with knowing that i could have done something but didn't. But what to do? I guess I have to know what it is I want. I'm just tired and bored of this and want it to end. No one else has confused me as much as him and I do not know why. I really want to stop with this nonsense and go get a life, go live my life, with no silly and obstructive thoughts or feelings getting in the way. It has gone on for long enough. He has affected me deeply and I want that to go. he played mind-games and power-games with me and I think he confused me with mixed or fake signals. What to do now? I have already told him how I feel via email, to get it all off my chest. Why couldn't I show my true colours to him, and why couldn't he see them, or see me for who I truly was? I also worry about he is doing and what he is up to now, sometimes, which is STUPID and a waste of time, I know. I just need to be in control of everything when I am upset, hurt, worried or scared, and maybe that IS normal. But the feeling is abysmal. I hate it. I don't know what to think and feel anymore. I just want to do things right. Untie all the knots and to make no more mistakes. I no longer want to be trapped by the same habitual ways of thinking and seeing things, of the same thinking patterns and perceptions that keep me stagnant, in the same place, and with the same boring problems, and from not moving on or seeing things differently. I want to get rid of my old self and my old ways. I want a creative and new solution. He has hurt me deeply in the past, and I want to get over it, as well as to forgive, for my own sake. I want things to be normal and clear again, instead of all these confusing thoughts and images in my head due to all these emotions. I just want to be myself and live my own life, be my real self and not put on personas or acts or be 'fake' due to insecurity, I want to be free to live my life without him in my mind, but I do miss him too, because I thought he was so special and amazing. I didn't know someone could drive you so crazy like this. And I wonder why. Maybe I already know the answers deep down but do not want to acknowledge them? Like I know that he just causes me pain for some reason or I cannot think straight with him, yet if he asks me to see him, I will go running, and it is sad, I am THAT attracted to him. Please someone, shed some light on this? Let me see normality and common sense again! I want to get my head straight and not fall into self-destruction, darkness and confusion! I just want to deal with things properly. I hope that soon, that one day I'll be able to see clearly and know what to do.