I am trying to find the poem, I'm sure by Longfellow, that refers to his long-dead wife "these eighteen years---" etc. Will someone help? Thanks

Paul, you are correct. It's from the Cross of Snow:

Henry Wadsworth Longfellow,

"The Cross of Snow"

In the long, sleepless watches of the night,
A gentle face--the face of one long dead--
Looks at me from the wall, where round its head
The night-lamp casts a halo of pale light.
Here in this room she died, and soul more white
Never through martyrdom of fire was led
To its repose; nor can in books be read
The legend of a life more benedight.
There is a mountain in the distant West
That, sun-defying, in its deep ravines
Displays a cross of snow upon its side.
Such is the cross I wear upon my breast
These eighteen years, through all the changing scenes
And seasons, changeless since the day she died.

Les