Darren suddenly didn't think her staying at Hogwarts was a great plan. They had to leave for summer, which was in a month! So Zoe had to go sooner or later, and she needed to learn occlumency in case the Death Eaters found her.
But Darren was just kidding himself, thats not why he wanted to teach her occlumency, for her own safety. He didn't care much, over the years he had become reckless, and he really only cared for one person. And even her, not so much anymore. It was mainly that they could use her as a big advantage against Voldemort. It was rather cruel, and he was quite sure she would disagree, but she had to do it. And she couldn't really spy on Voldemort without occlumency.
"Well, you don't have to leave them, if you know occlumency, you can go back there and just lie to voldemort, and he won't be able to read your mind. Then you can... remain safe there at Malfoy Manor, they won't hunt you down if your one of them," he said.
"I've already forgiven you for what you did, like I said, it was a stupid mistake, not inentional," he said. "But if you don't want to learn it, it doesn't matter."
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{btw, its funeral]