I know that when I had to let I had to focus on the most important thing, my happiness. No one can make me happy they can only increase my happiness. When I came to this fact I realized that if I loved a person I would want them to be happy with or with out me. I knew I was going to be happy with or with out them.
This is not a selfish thing. If a person loves you they would care that you are happy with them and they add value to your life. If they see you as an object you will eventually figure it out and then have to find the strength to separate yourself from that situation and move on completely.