somehow, everything i can think of are chinese folktales, like baishezhuan, or stories about fox fairies, flower fairies, bee fairies - tales right out of liaozhai. does keats's la belle dame sans merci count? some people think that if the knight hadn't listened to the pale kings and princes, she might have loved him. the only other thing i can think of is bluebeard, and that's got the roles reversed, and the monster spouse is metaphorical, of course. maybe i can find her something in wendy doniger on bedtricks and animal brides, although in most of those stories they know they're marrying a non-human. hmm.
su-lin is calling for sources and analogues to the melusina story. anything along the lines of: fairy or animal bride, injunction not to spy on, husband breaks promise, discovered to be what she is, cast out/transformed.