Cherish Memories But Nourish the Future
With grief for death, there will always be a piece of your heart missing but if you accept this and you're willing to carry the memories as lively as can be for the rest of your life, this will help you reach some acceptance of what has happened.
If it is a job loss or some other personal loss that is not death, you still need mourning time to release your sadness and grief over a loss of something that once filled a large part of your life. Doing something to signify the ending may give you a sense of closure and allow you to move forward.