…but the penultimate lines are:
“We are friends,” said I, rising and bending over her, as she rose from the bench.
“And will continue friends apart,” said Estella.
So, I am not sure, but I think what it is is that he will never part from her in his heart and soul, as deeply as she has been driven into it, and perhaps they will be friends, and he, at least will find a kind of peace with it all. Plus, you know how it is with Dickens sometimes. Maybe he is just implying they will meet in the afterlife.
If you want a truly satisfying ending, see Little Dorrit! And speaking of satisfying, so interesting that Bleak House is anything but bleak, and Satis house is anything but satisfying! Yet it will be razed to the ground and built anew. There’s hope there, I think!