Why and how does Pip betray Joe?

I'm not sure if this is the answer your looking for, but I've always felt it to be one of the saddest moments in the entire novel. In Part II, Chapter VIII, Joe visits Pip in London. He is uncomfortable, and Pip does nothing to ease his discomfort..... in fact, he makes it worse. Pip is embarassed by Joe's presence, his demeanor, his manors. He doesn't want to be seen with him, nor, does he want to be assicuated with him. Joe is a part of his past, and his presence in London is viewed by Pip as a threat to his new status as a "gentleman." During Joe's visit, Pip betrays everything about his relationship with Joe. The trust, loyalty, and love between them seems to be non-existent (on Pip's part). When Joe leaves, we know that he will never again visit Pip in his new life.