This question is really interesting. I mean, affection and love take many forms. In couple, especially a new one, lust and desire are melted with deeper feelings. With years, the ratio lust/pure affection seemed to reverse most of the time.
But if we think of other people around us (parents/child, friends, etc.), sexual desire is out the game, but love and affection are strong.
As Dio says, I think the story with the math teacher isn't over cause exept physical attraction, he was seduced by her sweet personality. With a touch of lust (growing again), he can be a real decent lover.
I prefer him than Dio and I just hope she's not going to drain him off desire forever, it would be sad.
I feel like our FL herself is confused with LOVE and LUST. Lust/desire is not permanent and it's definitely not love. When she asked do you desire me? she was asking the guy in terms of LIKE/LOVE when tbh the status bar is inclined more towards LUST & DESIRE. (Idk if that makes sense.) but anyone who sees the status bar completely drained from 100-0 would question themselves and the other person's motive or even their confession. She herself is a lil confused. ╮(￣▽￣)╭
Well, Duo himself said once the desire is drained to 0, they can genuinely start developing their feelings. So, what I'm guessing is...at first the status bar is more about superficial desire/lust and not love.