Wanting something else but still thinking the same way

What is it that makes a person want the same things even when they hurt you. No matter how much you want to believe it will be different, it might not be. You might have changed the physical, but the emotional is still the same. Your still the same person. What is it that makes the negative so hard to change and the good so hard to get? Why should it be so hard? No matter how much a person hurt you, you still don't want to walk away. No matter how much that dream is unrealistic, you just can't stop dreaming it. It consumes you. You can't let it be. A girlfriend of mine told me don't dwell on the past, what was meant to be will be again in your future. You can only take care of yourself and only strive to get what you need. But how do you quite your mind? How do you change your body's reactions when you can't control them? I am relatively happy with my situation right now. Don't get me wrong there are things that I am working on changing and I will continue to work on to changing but right now things are for the most part, good. So why is it that my body is reacting as though it's under a tremendous amount of stress? I'm dreaming about things and people who have hurt me in the past and there is no reason for it. I'm longing for situations where I wasn't happy and where I never wish to end up again. I can't help but have thoughts pop in my head of things which once made me smile and now make me upset. Is it a warning to be careful when creating this new life. Don't make the same mistakes again Jen. But then why do I miss those situations? Why does it feel better to be in those same situations even when the physical place and people have changed? How is it that my body's stress level lowers when I participate in things and with people who I know will eventually make me upset? I'm not being crazy stupid and doing things that are messing up the plan to get a better life but I'm starting to wish that our mind, and feelings had an on/off switch. It would make things a lot easier and sleep would be more enjoyable. AND WE ALL KNOW HOW MUCH I LOVE TO SLEEP. :)