Reason for that smile is nothing

Definition of "nothing".....

Time doesn't wait for you or me..
Days pass 'n year change,
You miss me.. I miss you,
You moved away with your loved ones,

Your life changes,
Friends change,
People change,

But your heart has
Those precious moments engraved in it
If you want it or not,
They are always their,

Making you sad at happy times
'N happy at sad times..

You think about those lovely
'N happy days than smile :)
'N when somebody asks you the reason for that smile..

You just say