The initial description of Joe by Pip in Chapter II of "Great Expectations" certainly connotes Pip's love and devotion to Joe as a small child:

He was a mild, good-natured, sweet-tempered, easy-going, foolish, dear fellow--a sort of Hercules in strength, and also in weakness....Joe and I being fellow-sufferers....

Later, in Chapter VII, as Joe explains to Pip why he married Mrs. Joe, Pip is touched by the genuine and kind feelings of Joe.  For, he tells Pip that when he looks at his wife, he sees his long-suffering mother, and is hesitant in being too mean to his wife.  He would rather, he explains, be too lenient than be cruel, adding that he hopes Pip will "overlook her shortcomings."  As Pip listens to Joe open his heart to him, Pip states,

Young as I was, I believe that I dated a new admiration for Joe from that night.  We were equals afterwards, as we had been before; but, afterwards, at quiet times when I sat looking at Joe and thinking about him, I had a new sensation of feeling conscious that I was looking up to Joe in my heart.

This admiration continues for Pip, for when he fabricates his visit to Satis House and Joe rolls his eyes, Pip feels "penitence" for having lied;

Toward Joe, and Joe only I considered myself a young monster.

He later confesses to Joe, who scolds him against lying; however, he encourages the boy by saying that Pip has intelligence and will become a scholar.  From his words, Pip is encouraged:

There was some hope in this piece of wisdom, and it rather encouraged me.

 Friend, father, and mentor--Joe is all these to Pip.