By Mary Gaitskill. But her confusion, which has developed into something of a theme in itself, is appealing. Two Girls, Fat and Thin,'' a dazzling, ambitious and ultimately messy novel, followed in 1991. Because They Wanted To,'' aren't generally as outre as those in ''Bad Behavior,'' with its cerebral prostitutes and its bewildered, eager masochists. They're out hunting for fulfillment, and they're less certain than ever that getting slapped around is the way to find it.
Sex is too complicated, it means too many things to people.
And it's what her characters are trying to get a grip on in their own sex lives, though often that grip falters. Valerie and Michael, the couple in ''The Blanket,'' get a huge thrill out of role-playing, but they nearly take their games too far. He's acting as much out of ardor as lust. I wasn't sure what she felt like to me. I was acutely aware of the artificiality of our experience.