How did Alec meet Viola and how did their relationship form? When did she realize how absolutely twisted he was?
Viola and Alec met when she was thirteen and he was twenty-five, when she was the golden child of an old and fading crime family and he was the up-and-coming right hand man of one of the most prominent crime lords in England. He caught her eavesdropping on a meeting, and although they both initially pissed each other off and each thought the other was full of themself, Alec found Viola entertaining and a kindred spirit in a few ways and Viola felt taken seriously by Alec and came to respect him in turn. Of course, he was absolutely grooming her. Their sexual relationship started when she was fourteen, and the more she fell in love with him and spurned other people, the more this formative dynamic got its hooks in her.
Viola sort of always knew that Alec was a bad person because of his job, because of his sexual interest in teenagers (like her), because of his open and unabashed sadism, among other things. Still, a few early moments helped her realize how twisted he is, such as watching him work, an incident wherein he had Viola assist him in raping another teenage girl, and his killing of his own brother. She has a love-hate relationship with his evil, but mostly it's love. She's a romantic that way.