It is human nature to hold on to negative memories for a long time and let go of positive ones easily. It takes conscious effort to overcome it.
When crises and setbacks occur, instead of feeling sorry for yourself, we need to overcome them. At times like these, we may not see any positives around. But that doesn't mean nothing positive is happening. It means we don't see it. You need to prepare your mind to see them.
Read good books, enjoy the arts, spend time with positive people, be more in tune with nature, start a new exercise routine, change your lifestyle. Change will be visible to you.
Allow yourself to emerge. Like a butterfly emerging from a pupa, overcome adversity and fly into life with colorful wings.