Probably the single most important characteristic of love is an empathy-driven willingness to make sacrifices (existential or material) in the name of helping a

Probably the single most important characteristic of love is an empathy-driven willingness to make sacrifices (existential or material) in the name of helping another person or preserving your relationship with them. Pretty much all betrayals of love ultimately stem from an unwillingness or inability to do so. That's at least true of all the reasonably clear examples of "not loving" that I can think of. Loving someone doesn't necessarily require that you make sacrifices but it does require that you would. That may be one reason it often takes a while for people to realize that they don't love or that they aren't loved. You never really know until it's put to the test. Maybe it's a single thing that's so significant, a loving person would obviously do or not do it. But it's probably more often a series of smaller things over time that individually seem ambiguous or minor but amount to a pattern.