He is besotted with her and her youth. She is pretty much besotted with his cock and becomes extremely possessive of this side of him, forbidding him to have sexual relations with his wife. Her jealousy gets the better of her and she threatens to cut off his member and keep it inside her. Meanwhile, their sex games are becoming more and more profane and they delve into asphyxiation games. Eventually these are taken too far and she strangles him, with his encouragement. She then cuts off his penis and places it inside her for keepsakes!
These scenes are filmed very graphically, but it is all lit and shown quite beautifully never diverging from the director's (Nagisa Oshima) mis-en-scene. In fact the whole glowing pallet and the tiny room locations add to the sexual frenzy, though the extreme relationship is never sexy.
As l'amour fou themes go, this is on the clinically insane side of the scale. It's certainly worth a watch, just for it's brazen, warts and all look. What makes it all the more bonkers is the fact that it's based on a true story!
She's only gone and done it!