How do I let go of her?

I really need to break up with someone but i cant do it. I know i have to and its going to be really hard for me because i know ultimately she wont even care. which makes me feel like crap. but she makes me desperately unhappy. despite this i feel like like i am still totally infatuated with her and this makes me want to be with her. i know i am a mug and a fool thats why i want to do something about it. How can i do it i cant bring my self to but i know i have to