Prompt: Nature
It wasn't in Macbeth's nature to let things go, but after a couple of weeks of enforced closeness with Erza, even he had to admit that continuously hating her took up a lot more energy than he really had to spare. Survival was just too damn hard with Jellal's methods, and the work they did was dangerous as well no matter how strong all the members of Crime Sorciere were. It was one thing to despise her in prison, with nothing else to do, and another entirely when they had to watch each other's backs during a fight with dark mages.
Furthermore… there was just something about Erza that he couldn't quite put his finger on, even knowing the gist of her history and how it dovetailed with his own (especially where Jellal was concerned).
Perhaps that was the root of his problems with her, after all.