When one person feels a very powerful emotional bond with another, which can be both reciprocal or unrequited. It is, at its core, morally neutral and can take on both positive and negative forms.

I believe its positive forms most often manifest to the fullest when both parties who share a requited love add mutual respect to the mix. Love without respect can lead to intense but negative behavior from the person who genuinely cares for the well-being of the other but generally feels the person or people they love is "beneath" them morally or conceptually.