I am not resigned to the shutting away of loving hearts in the hard ground
So it is, and so it shall be, for so it has been, for time out of mind
Into the darkness they go, the wise and the lovely; crowned
With lilies and the laurel they go; but I am not resigned.
Edna St. Vincent Millay, Dirge Without Music
Ginny's fairly certain she understands Harry better than anyone, which is precisely why she isn't outraged by his horrible explanation of why he's breaking it off. She knows what he's trying to say, and she understands why he's saying it.
She understands that this is something she cannot accompany them on, as much as she might like to. It is for the three of them alone, and she'd hurt them more than she'd help, because of the Trace and her inability to Apparate. Though she might appreciate a little more information about what they're doing, she knows that as more and more people learn a secret, the less safe it is. After all, who is she to say that she would not reveal it - whatever it is - while under the Cruciatus anyway?
After her first detention with the Carrows, she realizes that she might not hold up under torture. After her fifth, she realizes that she could and might go insane, like Neville's parents.
And she knows that Harry's decision to leave her has nothing to do with her safety, or either of them losing interest, but with the plain fact that Harry cannot be distracted from his task (she refuses to use the word destiny, as if he had no choice in the matter), and that she would be exactly that, a distraction.
She loves him (that's the difference between dating Harry and dating Dean), and she doesn't want to lose him, but Ginny knows that the odds are slim of Harry surviving this war. The Daily Prophet suggested that Harry was destined to defeat Voldemort, and she knows that it is both right and wrong. Harry is destined to defeat Voldemort because of his personality. He is as connected to Riddle as she is, and Voldemort has taken too many people and threatened too many others for Harry to do nothing when it is in his power to finish it. And she knows it is. She has no reasoning to explain it, but she knows.
She has faith in Harry, Ron, and Hermione to destroy Voldemort. Ginny decided that she would call him Voldemort when Dumbledore died. Of course, she now calls him You-Know-Who because of the Taboo, but in her head, he remains Voldemort. She did wonder if it wouldn't be more defiant to call him Riddle, or Tom, but once she saw him in the Department of Mysteries and realized exactly how inhuman he has become, decided he did not deserve a human name. If she thinks about the boy (man?) she knew from the diary, he is Tom. He was still human then, however twisted his mind.
Ginny doesn't know exactly what the three of them are up to, but she has a fairly decent guess. She knows Tom, very well (too well, she thinks sometimes), and she knows that he hates his Muggle roots and believes that dying is something like being a squib – a failure that isn't really your fault, but that makes you inferior anyway.
Ginny understands Tom Riddle better than anyone (with the possible exception of Harry), because when he possessed her, she was in his mind as much as he was in her hers. But she also knows that knowledge is a weapon, and that this task is not something she can share in.
She won't sit on the sidelines of this war, and so she made her own task. She resurrected the D.A, and with Neville, she runs it. Luna helped, too, but she didn't come back after Christmas, and Ginny can't help but to fear the worst.
But this is war, and they can't afford to stop fighting and mourn. They have to protect the children here from the Carrows and she will do so, no matter how many times she gets hit with the Cruciatus or gets whipped or stuck in the dungeons. She and Neville share that grim understanding that it's better that they get tortured than an 11-year old whose only crime was misunderstanding.
Sometimes Neville reminds her too much of Harry, and she has to bite back the flood of emotions that never fails to arise at these times. She may have had a crush on the Boy Who Lived at 11, but she fell in love with Harry at 15 (she knows she's young but she can't trivialize her feelings by saying she merely fancies him). But part of the reason why she fell in love with him was because he was the Boy Who Lived – every bit as selflessly noble as her 11-year-old self could have imagined.
As the days go on, more and more of the lies she told herself to get through it are stripped away. She supposes it's a side effect of torture – pain makes you reevaluate your priorities.
One day, as Alecto Carrow smirks down at Ginny in between bouts of the Cruciatus (she's saying something along the lines of "Not so bloody lively now, eh?") Ginny lets go. She can't pretend she doesn't love Harry; she can't pretend she doesn't know anything about where he went; she can't pretend she isn't enduring this for him (she could manage an escape to rival Fred and George's, if she chose). And even if she could, she doesn't want to.
She was stupid, she thinks, to imagine she could undergo the Cruciatus as though it were a particularly difficult Quidditch practice – that she could simply grit her teeth and ignore the pain.
No, she thinks as Alecto puts the curse back on, this pain will not be ignored, and she screams (she thought she could hold back those screams, before she'd ever had the curse put on her). And if she's under long enough, it's not even about holding on for Harry anymore; it's just about survival.
Afterwards, in the common room, she sees that same realization on the faces of her fellow classmates and D.A. members. When Neville (brave Neville, who has lead them so well this year) asks her if she's all right, she pauses.
"Define alright," she says in a voice that rasps from screaming.
Neville opens his mouth, shuts it, and says, "Are you in need of emergency medical treatment?"
This phrase has become something of an inside joke among her friends because of the frequency of injury in both detentions and D.A. practice sessions, and so Ginny dutifully laughs and shakes her head, even though she doesn't really think it's funny.
It's just another reminder of how different things have become. Last year, she wouldn't have dreamed of Hogwarts perverted like this. Last year, the worst detention she'd ever had was when Snape made her disembowel three barrels full of horned toads (without gloves) because she Bat-Bogey-hexed Malfoy. This year, it involved running away from a pack of bloodthirsty werewolves in the Forbidden Forest.
This is war, she thinks. She loves Harry, she just might lose him, and there's absolutely nothing she can do to change that. She will continue to fight, because that's all there is to do.