In The Sun Also Rises by Ernest Hemingway, does Brett intentionally hurt Jake, or is this just a by-product of her own blindness?

This is open to interpretation, but most would say that Brett hurts Jake not out of blindness, but out of her own selfishness. Whether she intentionally tries to hurt him or not, she puts her needs (in this case, her needs to be satisfied sexually, which Jake cannot fulfill) above Jake's emotions. She essentially uses Jake for emotional support, giving him brief glimmers of hope before reminding him (verbally or through obtaining a new man of the hour) that she can never return his love. She knows Jake's feelings for her, and though she loves him on an emotional and intellectual level, her selfishness is what makes her continue to string him along, therefore hurting him.