Daguerreotype
D023

Inside the case:

"If I had thought you could have died
I might not wish for it
But I forgot when I thought
That thou couldst mortal be
It never through my mind hast past
the time would e'er be over
and I on thee should look my last
and thou shouldst smile no more
- - -
Though fate induced that we should part
and each forced to sever
still thou remain in my heart
............ never "

On the paper, front:

"My initial one
No one shall fill
the hole thou had
left vacant in
my heart"

On the paper, back:

"How dear is
this to me it
is all I have left
my first my last
my only love
my last idol"

It is signed with a date or a name, but it's too hard to make out.

The first part inside the case is a known poem called "To Mary".
It's by Irish poet Charles Wolfe (1791–1823), best known for
"The Burial of John Moore after Corunna" (1816)

The original goes as follows:

If I had thought thou couldst have died,
I might not weep for thee;
But I forgot, when by thy side,
That thou couldst mortal be:
It never through my mind had past
The time would e'er be o'er,
And I on thee should look my last,
And thou shouldst smile no more!

The rest of the poem can be found here.