The spirit cannot die. It can only choose to leave the body in order to get rid of adverse circumstances on Earth. If your loved one has died, a part of his energy is likely to remain with you till you release it.
Spirits who die fighting in war or at home etc continue fighting after rebirth till healed,calmed and released by the spirit releasement, Theta healing and past life therapies.
The spirit cannot leave if you keep thinking of it. Hence, it is better to let the memories of the form go than hope for that person to remain in that particular body form, as the spirit does not have that body anymore. If you keep calling the spirit, it enters your body because a spirit without a body becomes like a homeless man and needs your support constantly to live on; but it does not feel happy staying on with your support as its own soul has no purpose left to live on. It only stays to take care of you as it feels being constantly called. Parts of the spirit which remain attached to you remain negative.
The spirit continues future lifetimes in the same worries till healed and released. It affects the bodies it is attached to and its future births with making them excessively focused on negative aspects of life,anxieties and depressions.
The following is an excerpt from my book - Redefining Happiness- chapter on spirit release therapy.
If you feel overtly negative or depressed or have excess weight, you may be holding spirits in your body of dead or alive people you were once attached to. Spirit release helps in moving to a more positive state of mind.
Death needs to be taken as the soul shifting from one place to another. If death happens early in life, it may mean quitting a class half way. Hence, if we have the energy left to live, it us better to complete soil lessons in the present life , learn forgiveness and peacefulness and feel content than carry over lessons to the nect life.