Pip has spent most of his life in a passionate love for Estella. At the end of the book, he sees her again after an eleven year absence. Dickens brings their relationship full circle in that the first place he fell in love with her is the last place he sees her in the book. Pip even comments on that. He says,
"After so many years, it is strange that we should thus meet again, Estella, here where our first meeting was!"(pg 450 - chapter 59)
She is greatly changed, but it doesn't matter to Pip. He still loves her. He says,
" The freshness of her beauty was indeed gone, but its indescribable majesty and it indescribable charm remained. Those attractions in it I had seen before; what I had never seen before was the saddened, softened light of the once proud eyes; what I had never felt before was the friendly touch of the once insensible hand." (pg 450 - chapter 59)
Notice that she has changed. She is offering a friendly touch. She has come to acknowledge that she threw the love Pip had for her away, and she did not recognize its worth. She recognizes it now. She says,
"There was a long hard time when I kept far from the remembrance of what I had thrown away when I was quite ignorant of its worth, but since my duty has not been incompatible with the admission of that remembrance, I have given it a place in my heart." (pg 451 - chapter 59)
So, yes, they do part friends, but the "parting" is ambiguous.
Pip tells her that she has always had a place in his heart, something the reader definitely knows. Estella asks Pip,
"I have been bent and broken, but ---I hope --- into a better shape. Be as considerate and good to me as you were, and tell me we are friends." (pg 451- chapter 59)
Pip replies, "We are friends"
He then takes her hand and they walk together out of the ruined grounds of Satis House. This is definitely a friendly gesture. However, Dickens leaves their relationship a little ambiguous. She says "And we will continue to be friends apart" , but Pip observes in the last sentence of the novel, "I saw no shadow of another parting from her." (pg 451 - chapter 59)