>>281817032
Fumiko is a servant and a survivor by nature and she's just looking for a strong Devil to align herself with. Right now that appears to be Yoru.
She's too cunning and fully invested in her schemes to be swayed by her likes or dislikes. Everyone is simply a means to an end for her, even if she likes them.
She also knows that getting romantically involved with Denji is a death sentence, especially to someone like her who has a weak body, despite her cloning ability. She's clearly concerned about her declining number of clones and tries to preserve them.