Can you still be tsundere if you totally lack the dere part? Aren't you just an abusive possessive asshole then? I mean, to me, there's a difference between love and obsession/possession, and at this point I'd never say that guy loves her.
IMO, tsundere needs dere part to be a tsundere, even if the dere part is twisted, toxic or unhealthy. Since the mini spoiler says that he actually has some level of interest in FL, whether or not it's romantic or something else, I'd say he has the dere part too. Dere to me also isn't just limited to romantic/sexual feelings but also for familial/companionship etc more about attachments, because otherwise the bro-con sis-con parent-con tsunderes and yanderes wouldn't make good sense. For love vs obsession/possession, let's just say extreme cases their idea of love is not really the same as what average people see love as... and so perhaps their love would include obsessions/possession.