" . . . relationships are not fixed. They continually change. The person who is kind to us today isn’t kind to us the next day. The person who is mean to us today is kind to us the next day. And so because everybody has harmed us at some point, and everybody has helped us at some point, then there’s no reason to cherish some beings over others, or hate some beings over others. Everybody has done everything to us before. It is very helpful to think like this.
"If we’re able to free ourselves from this attachment, aversion and apathy, then we automatically avoid something that most worldly people consume a whole lot of time in, which is helping their friends and harming their enemies. When you look back at your life, how much time did you spend helping your friends out of attachment, not out of genuine sincere love, but out of attachment to get something back? How much time did we spend harming the people we don’t like?"
~ Ven. Thubten Chodron, "Cultivating Bodhicitta through the Seven Points of Cause and Effect – Part 1 of 4"http://www.thubtenchodron.org/GradualPathToEnlightenment/articles_and_transcripts_of_teachings_on_lamrim.html
May this be of benefit.