Lily thought about the time he said they could have forever.
She thought about how, one night in their seventh year, they spent the night wrapped in each other's arms. That night, the night James had gotten the letter announcing the deaths of his parents, she went up with him to the dormitory that him and the other Marauders shared when he said he was tired. She hadn't meant to stay there for the night, but when she said goodnight and turned to leave and he called out for her to stay, she knew we wouldn't leave him alone. She couldn't.
They drew the curtains on the bed closed and casted a silencing charm around the bed so they could talk without waking the other boys that would be coming up to bed in a couple of hours. They both laid down on their sides, facing each other, and she slowly lifted her arm to lay her hand on his cheek. He squeezed his eyelids closed for a moment and when he opened them there were tears threatening to spill over.
"I... I just..." he stammered as the tears spilled over. "They're gone."
"I know," Lily said softly while stroking his cheek with her thumb. "I'm sorry."
He leaned his face closer so that their foreheads were touching and continued to silently cry. Lily held him while he wept for the loss of his parents, and as the tears began to slow, he began to talk.
He spoke of stories about his parents. Some were pleasant, like memories of shopping trips in Diagon Alley, and some were not, like the massive fight he had had with his father during the summer after his fourth year. Most were just small things, like habits or phrases, his parents had had. Things that he said had seemed unimportant at the time but we're now all he could think of. He talked for what seemed like hours on end, but Lily was glad to be there to listen to every last word. He talked faster as he went as if he was desperate to get the words out, and he sowed no signs of wanting to stop until suddenly, in the middle of a story about his mother's famous chocolate pie, he stopped.
"James?" Lily asked.
"How can I do this?" he asked, sounding more lost and broken than Lily ever imagined he could. "I need my parents."
"I don't know, James. I wish I had a better answer. I suppose you just need to ask yourself how they would have wanted you to. How would they have wanted you to go on without them?"
"My mother used to say 'just keep loving.' Anytime I'd had a bad day that's what she would say to me. It was like her version of 'just keep going.' She would have wanted me to keep loving."
"Then that's what you'll do," she said. "You'll just keep loving everyone else in your life, and you'll just keep loving your mum and dad even though their gone."
"Lily," he whispered. "I love you."
Her heart skipped a beat. He'd been proclaiming his love for her since first year, but this was the first time he'd said it like this. Like those words should be spoken. Not like a joke but like a promise.
She found it was easy as breathing to say it in return.
"I love you too."
He let out a sound that was half laugh, half sob, and curled into her. She stroked the hair on the back of his head, and they laid curled up like that until he whispered, "Can you talk about something else? I can't think about that anymore. I'll lose it."
"Of course," she responded. " what do you want me to talk about?"
"Anything. You, me, us, whatever. Just not that."
"Alright," she said, "I suppose I could tell you that I liked you a long time before I finally said I would go out with you. I probably started to really like you around the beginning of sixth year. I was just too stubborn to let you know that you were right all along about me eventually going out with you."
"All that extra work you forced me to do, Evans," he said in the lightest voice he could manage. "I had almost given up."
"Well I'm glad you didn't," I said, then paused. When I spoke again it was soft, "I wish I hadn't waited so late to tell you how I felt. If I hadn't been so stubborn it would have meant one extra year of this. Of us."
He lifted his head from where he had it tucked on her shoulder to look her in the eye. "That doesn't matter. An extra year doesn't matter. We could have forever."
She leaned forward and placed a kiss on his forehead, his nose, and finally his lips before she answered. "Yes, James. We very well could."
They curled back into each other with James's forehead against her shoulder, her arms around his waist, and their legs intertwined, and she whispered comforting words to him until they both drifted into sleep.
That was the night Lily thought of when she heard the high pitched voice cast the spell.
"Arvada Kedavra!"
That was the memory Lily's mind conjured when she heard her husband's body hit the ground.
"We could have forever."
They could have had forever. Her and her little family. Forever to laugh and play and fight and make up. Forever to just keep loving each other.
That was all Lily could think of as she turned to face the man who took everything from her. The man who she was fighting to destroy.
James may not have had forever. She may not have had forever. But Harry still could. And she could give him a chance at that.