When Villanelle describes her love for Henri as both “brotherly” and “incestuous,” she means that she has both familial and sexual feelings for him—but not passionately romantic ones. As Villanelle experiences passion as a loss of self-control, symbolized by the loss of her heart, she expresses her lack of passion for Henri by saying that he would be unable to steal his heart. Sadly, Henri has never felt passionate love for someone he could expect to return it—Napoleon, for instance, could not reasonably be expected to return the love of each individual one of his soldiers. Still, given how badly Villanelle’s reciprocated passion for the woman with gray-green eyes turned out, it’s not clear that reciprocated passion would have improved Henri’s life, either.