At the least, I would imagine we would have 3 categories: Platonic love, familial love, and romantic love. You may love all of these people, but they are different kinds of love. I would say the common requirements between the three are trust, respect, and common ground. The common symptom would be exceptional loyalty. It also seems reasonable to me that they aren't all equal, but that it varies by person. Love is hard for me to define sweepingly, there's some things about it that I'm not sure how to qualify. This is about the best I can do. I really hope this one continues though, "What is love?" seems like it could generate an interesting conversation.