Well it seems a little oxymoronish to Kill and be Kind at the same time.but being kind is the right thing to do, maybe instead of killing them they will learn to be kind also, or just be kind in return. The Golden Rule if you will.
The person might not be who you thought they were; might have changed for the worse; but in the memories, they will always be the person you loved. it's ok to cherish those memories. You dont have to allow that person in your life now.