The Joker obviously isn't the loving type. He's cold and sadistic. But with Harley he feels omething he doesn't often feel. At first she was a pawn, used to help him escape but she went further for him than any other girl he's ever seduced and for some reason he didn't kill her like the rest. His obsession with Batman has taken over his life but he can't live without Harley either, his cuore is small and messed up but I think he does care. Sometimes it's just the power he has on someone but he does feel something there and constantly refuses it. But I believe it's there :)
Personally, I think that he isn't sure. Many people believe that violence was the largest part of their relationship, but that is not true. I think that the violence part comes from the joker not understanding his emotions for her. He knows that he doesn't want to Amore her, but for some reason he will always keep her around. He needs her. But at the end of the giorno the joker is too obsessed with Batman to even pay attention to Harley.
I think he does but in his way. He liked her because she is helpfull (sometimes) and is a distraction for batman. Well i don't think harley is in Amore with him......that is not love¡ she is just a psycho that is trying to complace feelings of release because she have a difficult life....poor harley :( but both of them are great togheter and his "love" is something to be proud about ;)