"Lianna" comes out of the closet, buck naked. Hers is a low-budget, low-key story about women in love with women. But more than that, it's about how one Cinderella kicked off her glass slippers along with her complex. "Lianna," written, directed and edited by John Sayles ("Return of the Secaucus Seven"), is a good film, but not a film for everyone. It's explicit, erotic and more realistic than "Personal Best," which dealt with homosexuality as if it were temporary insanity. In "Lianna" it's for keeps. Its screenplay bubbles like a soap opera, a sudsy concoction of adultery and sacrosanct liberalism. It follows a wan, weak academic wife (Linda Griffiths) from her unhappy straight marriage to her first gay love affair. Lianna's husband, Dick (Jon DeVries), is an abusive brute. He's as hateable as J.R. Ewing, else we might not accept Lianna's sudden change of heart or her love scenes with Ruth (Jane Hallaren). (The first scene between the two women is trashed with a soundtrack of frenetic French: Je t'aime. J'espere. Je t'aime. Je t'aime.) After learning of their affair, Dick -- no stranger to adultery himself -- throws Lianna out and keeps her from their kids, Theda, 8, and Spencer, 13. Lost and jobless, she turns to Ruth for salvation. That's when she finally realizes "I gotta be me." She sees that Ruth and Dick may be opposite sexes, but otherwise alike -- two uptight professors interested in women. Viewing the film, with its documentary technique, is like invading privacy. The script is lifelike, graphic and strong: "So my old lady's a dyke, big deal," says her son (Jesse Solomon). He's the film's worst actor -- except for Sayles, who cast himself as a hot-to-trot cinematographer. But somehow, the clunky acting and uncomfortable players make it seem all the more like creeping through someone's messy house.