What did Santiago find humiliating?

You didn't cite a section here, so I'm going to give you a few different answers......

1) he found his life ashore humiliating; he had nothing..... he didn't even have the help or companionship of the boy he loved because of the 'bad luck'

2) he is humiliated that his left hand cramps us and refuses to work the right way for him; he tells it to go ahaead and turn into a useless claw.

3) at the end of the novella, Santiago feels shame and humiliation because he failed.