I think "clinical depression" and "grief" are often confused with each other and the symptoms of one can be attributed to the other. Grief following the loss of a loved one can last many years, especially if the death happened in circumstances far away, where you could not be with the person when they died, or if it was a particularly distressing end. Feelings of sadness or unjustifiable guilt can suddenly jump out of nowhere and ambush you unexpectedly. even when everything else in your life is calm and unstressful. These are quite normal human emotions so don't beat yourself up about them. In time they will lessen and happen less frequently. You say you have now retired so your pace of life has changed and perhaps now with more time on your hands you have more time to think and reflect. Sometimes that inevitably leads to thoughts of the past and some of these can be sad. But now it's time to think optimistically about the future, joining new groups to make new friends or learn new hobbies and skills. So let hope now rise from the ashes and look ahead with optimism to the future.