I Samuel 16:1

"And the Lord said unto Samuel, How long wilt thou mourn for Saul, seeing I have rejected him from reigning over Isreal?

Has someone you loved left you? I mean have you broken up with someone, divorced or have people just left your life and refused to have contact with you?
That can really hurt. Especially when they have alienated themselves and you feel like we haven't done anything wrong.

Know that as in Samuel, in God's eyes, they are "rejected" for your life. It does not mean they are a bad person. It just means that they are not needed to help you reach your destination.
Do not mourn over your "lost" love. It can only hinder the work that God has for you to do and possibly make your healing take longer. What do you think?