How do i break up with my girl when she loves me already?

Alright, here it is, i've been with her for almost a year now. I'm crazy. wrong in the head. very emotionless in most aspects yet when it comes to breaking women's hearts it's a different story. before when i was 17 i would cheat on women and get caught on purpose so they would break up with me so they would be angry instead of sad which brought me comfort. You could say I used to be pretty promiscuous and have slept with about 30 plus women, i've just now turned 22, i slowed down production now that i'm with my girl, only sleeping with about 1 or 2 different women every few months. My girlfriend loves me. I tell her i do as well. When i first met her i knew i wanted to bang, but my thoughts never went beyond that. I love the thrill of the chase, getting new cat, obtaining the heart, but i do have a short attention span. Very rarely have I ever been interested in someone longer than a month. when i am, it's ironic that it never works out. I can't seem to get my exact counterpart, not to sound arrogant. I'm a funny guy or so everyone tells me but all i am is just honest. I have no remoarse when i cheat, the only times i have is when it wasn't a hotter chick than my girl. I know. I'm terrible. I'm sick in the head. Background history, i was very shy with women as a teen, once i figured all i have to do is talk to them it all became too easy. I love conquering, love getting more. I have two twisted sides, my righteous church side that knows i am wrong. and my twisted side, the one that was born out of living in reality, where i saw dysfunctional couples and women and men cheating on each other. I knew then i would never put my heart in a relationship. I like my girl but i am tired of her. She knows the right things to say. Yet, i want more. i don't know what i am. I'm a monster i know. Yet there is still a good side of me though only small traces remain. I don't want to hurt her. I don't believe i love her or i would not be seeking out more women. something that may be good to know is my hero is Julius Cesar. I have an unquenchable thirst. Yet at times it's just merely to test myself. I'm not the same as i was at 19. Then i was much worse. What should i do. i don't see myself being the 9-5 come home to the wife and annoying children that are a mere reflection of the monster that i am. I don't want that. I see so much more and yet i can't grasp the already faded dreams of yesterday. I want more and more, yet i don't want to loose my girl for the mere comfort of having someone though life can be mundane with her.