Is it permissible to keep a picture of a girl you loved and wanted to marry but were not destined to be with, knowing that you are now married and have four children, and she is also married?

It is forbidden to keep pictures for remembrance, due to the Prophet's (peace and blessings be upon him) saying: "Angels do not enter a house in which there is a picture." The sin is greater if the picture is of a foreign (non-mahram) woman and she is married. The questioner must repent, tear up or burn the picture, and repent if any Sharia violation occurred with the subject of the picture.