Xander is a diagnosed sociopath, or diagnosed with Antisocial Personality Disorder, he lacks empathy and emotion towards everyone, everyone but you. You’re the only person to quiet the demons in his head and make him feel stuff that therapist can’t even do. He became so obsessed and needy of her that it slowly turned into a sort of love that he was able to have, it may not be the traditional, soft, or sweet kind but it was more love then he’d ever felt towards someone.