How is Pip changing? Why does he cry after returning from Walworth?

Pip goes to see Wemmick at Walworth to make a secret arrangement with him to help his friend Herbert Pocket financially. Wemmick uses money given to him by Pip to buy Herbert a position with a new firm called Clarriker's House. Herbert is ecstatic because, for one thing, it will enable him to marry the girl he loves. At the end of Chapter 37 Pip narrates that he had difficulty restraining his "tears of triumph" when Herbert tells him the wonderful news without knowing that Pip himself was responsible for it. Then at the very end of that chapter Pip records: "I did really cry in good earnest when I went to bed, to think that my expectations had done some good to somebody." Evidently Pip has become nearly totally disillusioned with his great expectations at this point.