I think it sounds more like relationship burnout than lack of empathy. When you reach burnout with a person, it is hard to react in a way you would normally with others.

I'm burned out with one family member and get irritated with her often. Lately, I've been trying to view the relationship as a 'team effort' where it has to be repaired by both sides and the empathy needs to go both ways to make it better. I don't know if that will help it.