It was difficult to fight with Luna Lovegood.
He could always think of something cruel to say, that was the easy part.
The problem was actually getting a response from her. She would come skipping along on a day when he was in a particularly difficult mood, sit next to him in public where anyone could see, and let loose a torrent of mindless chatter.
'Merlin's sake, you really are bloody loony. I don't want to talk right now.'
Her face would flick through a myriad of expressions in the space of a second, from blank and full of daydreams, to confused and a little hurt, ending in sudden understanding.
'Oh, that's okay Draco, you can just listen!'
Some days he might respond, try and push for a fight, because God it just frustrates him how she can be so positive after everything! How she can claim that she is 'almost entirely certain I am in love with you, because it feels all warm and fuzzy!' when he tormented her for years, tortured innocent people, and could still be so pointlessly cruel... but it barely ever worked.

When it did he just felt guilty and unclean.

She was so innocent; there was no joy in breaking her. He would gaze into her eyes filled with silvery water, the embodiment of the hurt that she never allowed herself to show.

(Because she doesn't care, she doesn't, she couldn't.)

He would watch the sunlight bounce from the lake and entangle itself in her hair, remembering what it felt like to run his fingers through, how she made him feel.

Late nights in the astronomy tower, with her back against the wall and her breath on his neck, soft skin and baggy clothes. Whispered words, from sadness to joy. Smiles that passed from her to him, and were licked off of one another's lips.

She was so innocent.

'I don't want to ruin you.'
Her laughter was loud and quick, no tinkling giggles.
'Then don't. Don't ruin me. Give me a gift, a good memory for us to keep, so that we can start to balance out all of the bad ones.'
She was so much better than him. She wanted him.

(Snatched moments.)
Long conversations that languished on the grounds, in the forests with the thestrals, on a tree that she declared was theirs.

It was difficult to fight with Luna Lovegood.
Today she did not skip up to him.

He leans with a practiced nonchalance against a tree on the edge of the grounds (not their tree, just an ordinary tree) as if he is not waiting for her; even though they both know that these meetings stopped being coincidence over a year ago.

She walks with trembling determination sketched upon her face. She doesn't kiss him, she doesn't float or fidget, she stands with a practiced stubbornness.
'I understand why you don't want to be seen with me... It makes perfect sense actually, when I pretend that I am inside of your head. If I am you, which we are pretending that I am right now... then I have already fallen rather far from where I was a few years ago. People are not quite as scared of me, or at least they forget to be until I actually threaten them. Now imagine if everyone heard that I was spending the majority of my time with Loony Lovegood, voluntarily.'
She paused for breath and looked up to meet his eyes. She had done quite well at being angry until that point; he would have to comment on that at a more appropriate moment. She was still his Luna though, and her anger never lasted long.
Her tiny hands grasped his arms, her feet stretched out so she might be a little closer to his face. He made sure to tense his muscles so she wouldn't fall.
'I don't blame you Draco, not really. The origins of your actions are really quite traceable, and obviously I did initially condone this, sneaking around is fun isn't it? Like an adventure!'
Luna went into contemplative mode, (her eyes get even wider and her mouth goes very small, as if to compensate for the lack of room on her face.)
'A few people do know now, though. I know you punched Theodore Knott in front of everyone because he said I looked like a drunken gnome, plus it turns out Ginny can't keep a secret and my friends were always the most likely to object...'
She teetered on the edge of her toes now, he held her closer, still not saying a word. Might as well let it be calm before he has to break her heart, again.
She kisses him on the cheek with chapped lips, then whispers in his ear.
'I'd like to stop sneaking around now, please.'

Much to Draco's unending shock and disgust, little loony Lovegood was the sanest person he had ever known. But she could not come to dinner with his parents, and he could not go to parties with her friends. She provided stability, and if he needed to say a couple of meaningless words to keep her around, so what? It wasn't like he meant it. (He doesn't, he doesn't, and he couldn't.)

Luna was lovely in private, but never in public.

'Look Loony...'
It was difficult to fight with Luna Lovegood.