What is the best thing to say to someone who is taking you for granted.?

i've been with my g/f for a few years yet she takes me for granted and i'm super tired of it, that im on the brink of breaking up with her. it is so frustrating because i do love her. How or what can i say this and phrase this correctly, one thing i don't want to do is do a guilt trip on her. i don't want her to change because of guilt i want it to be because she realizes the harm its doing to our relationship. Can anyone help me?