Shego didn't always know why she'd stuck with Drakken. But mostly she didn't understand why he'd kept her around. How, despite every opportunity to hate her, he never did.
He was evil enough, for a geek, but she could be… cruel. Even when he didn't deserve it.
Sometimes he snipped back at her, or snapped at her to "shut up!" but he rarely got upset with her day-to-day attitude. She didn't mean to be, well, mean, she just… didn't know how to be better.
He should hate her, but somehow it was, "I love you," being murmured in her ear.