When someone loses a person or pet in their life to death, for whatever reason, there is a void left. There are so many thoughts & memories. Sometimes, even anger for the "leaving". And of course there is the sadness & heartfelt pain. Take peace in knowing that your lost one will always be with you. When the vessel, or body can no longer survive, the spirit lives on! Take time to mourn, find closure and allow yourself to have sad moments, but know that "they" wouldn't want you to continue to be sad. They love you and want you to continue on with life. You will never forget them, that's not a possibility.
I can tell you from personal experience that it is never easy, but I know they would hope for more smiles than tears of sorrow.
Smile when you think of them and live life!