What I'm trying to convey is the desire not to do harm to another person because you value not harming people.
"Respect" is almost there but it carries the additional meaning of respect for authority and sort of implies an unbalanced relationship.
"Empathy" also captures something of this but empathy seems more about emotions that are shared rather then behavior.
"Concern" also feels wrong as it seems to be too fleeting.
If I was to use it in a sentence it would be something like "The moral of the story is that a relationship without XXXX results in tragedy no matter how much the people involved love each other".