Not being able to say goodbye

Why? 
Why is it that i still want to know regardless of how much you make me feel dead inside, regardless of how much you hurt me so often 24/7. Having you in my life makes everything a billion times worse, and what angers me even more is the fact ive had the courage to say goodbye to everyone who hurts me apart from you. I'm so stupid, why i do that i don't know.
In every way i am coming so so far with everything and im feeling so great about it, but then this is one of the small things that is holding me up. I love being able to write here, because i know for a FACT you will not see it. As much as i sit here saying i know i need you out of my life, i actually dont have the guts to do it, and the thought of it makes me feel sick to the stomach.
I wish i could walk away and say to myself that its not working no more, and that this relationship brings me nothing but hurt and tears, but you know what i can't....I've known you for so long now, you are a PART of me, and even though i don't want to 'offically' be with you, i hate to see you with another girl...it gets me so jealous it's unreal. I hate that feeling, it makes me hate myself for feeling a feeling that is horrible and not pure and good about someone. I will go on your facebook and look at pictures of her, wondering what it is about her that makes you so happy and what i did wrong...all i have ever done is love you and be there for you.
Friendships and relationships are incredible, they change us so much for the good and for the better and i know that i am constantly learning from everything that happens, but from this i really am getting nothing but hurt. I'd admit that in a heartbeat but not to you, not to your face. I want you to be happy of course i do, and i want to be happy but im scared of loosing you from my life because i actually dont think i could live without you. 
I need someone to come along and block and delete you in all ways possible, you asked me a few days back, was i ok and that i was acting like an idiot. that hurt, but then i guess its true, you didnt even wait for an answer though. 
I need so much strength for this, im coming so far with all my other problems, it's just this one thats getting in the way...