Sympathy is when you feel badly for your partner or when you’re sad for your partner if something bad happened to him or her.
Empathy, on the other hand, is being able to actually understand your partner’s perspective or situation to the degree that you can identify with what they are feeling and why.
If you sympathize, you feel for someone because of his or her pain. If you empathize, you feel his or her pain with them. For example, Kate doesn’t just sympathize with Brian because he had a difficult childhood.
She is able to imagine what it must’ve been like to have a chronically ill mother and a depressed and withdrawn father. She understands that Brian, given his family problems, lived with considerable uncertainty.
by Jeffrey Bernstein