This is a pretty pitiful read. Watanabe is just using Amane for her own amusement and fetish. Amane keeps catering to her every whim because he loves her. She doesn't love him back, however. He's just a voice automaton for her. Her approach is, in fact, quite sadistic toward him, as she doesn't give a damn about his feelings when he's forced to use the girly voice, which cause him to be bullied. If you do consider sadism a sign of love, then maybe she does like him, who knows.