Is it true that "Great Expectations" was originally written with an
"unhappy" ending (Pip doesn't marry Estella), and where can I find
that original ending?

Hello annek,

Yes, it is true.  Here is the original ending that Charles Dickens
wrote for Great Expectations:

"Dear Pip," said Biddy, "you are sure you don't fret for her?"

"I am sure and certain, Biddy." 

"Tell me as an old, old friend. Have you quite forgotten her?" 

"My dear Biddy, I have forgotten nothing in my life that ever had a
foremost place there. But that poor dream, as I once used to call it,
has all gone by, Biddy, all gone by!"

It was four years more, before I saw herself. I had heard of her as
leading a most unhappy life, and as being separate from her husband
who had used her with great cruelty, and who had become quite renowned
as a compound of pride, brutality, and meanness. I had heard of the
death of her husband (from an accident consequent on ill-treating a
horse), and of her being married again to a Shropshire doctor, who,
against his interest, had once very manfully interposed, on an
occasion when he was in professional attendance on Mr. Drummle, and
had witnessed some outrageous treatment of her. I had heard that the
Shropshire doctor was not rich, and that they lived on her own
personal fortune.

I was in England again -- in London, and walking along Piccadilly with
little Pip -- when a servant came running after me to ask would I step
back to a lady in a carriage who wished to speak to me. It was a
little pony carriage, which the lady was driving; and the lady and I
looked sadly enough on one another.

"I am greatly changed, I know; but I thought you would like to shake
hands with Estella too, Pip. Lift up that pretty child and let me kiss
it!" (She supposed the child, I think, to be my child.)

I was very glad afterwards to have had the interview; for, in her face
and in her voice, and in her touch, she gave me the assurance, that
suffering had been stronger than Miss Havisham's teaching, and had
given her a heart to understand what my heart used to be.

"Discovering Dickens - A Community Reading Project - Great
Expectations - Notes on the Novel: Issue 18"
Stanford University
http://www.stanford.edu/dept/news/dickens/great_issue18gloss.html

You can compare it with the revised ending, shown here:

"Great Expectations - Revised Ending - Chapter 59"
Skaneateles Central School District
http://www.scs.cnyric.org/RevisedEnding.pdf

- justaskscott


Search terms used on Google:

"original ending" "great expectations"
"original ending" "dear pip said biddy"

Excellent answer, very good sources. Thanks.