She can't believe she trusted him again. Once again, she fell for the Fred Weasley charm and the Fred Weasley eyes and the Fred Weasley everything else. He pulled her back in, and she hates him for it.
It's the same scene each time. He comes crawling to her, so filled with loneliness that she has to take pity on him as he tells her his cliché tragedy. He fills her in on the intimate details of his self-loathing and insecurity, and she, without a thought of the consequences, steps up to become the friend he so clearly needs. Despite his consistent record of disappointments and failures, she chooses to spend her time trying to fix him because she has convinced herself that underneath all of his bravado and stupidity, there might be a halfway decent person hiding.
Time after time, he comes to her with some pathetic "secret self" and she subscribes to his façade. If he's busy or exhausted from Quidditch practice, she pulls late nights and writes his essays in addition to her own. When he doesn't do the things he ought to, she lies to professors and forges signatures. Sometimes, when he's lonely, she lets him pull her in close and she kisses him like she means it.
And she did mean it. She meant it for six long years, but she doesn't mean it anymore.
For the first time, she's going to be the one walking away.