Complex sentence: When Sadie offers to help, Jake initially refuses, fearing that the "obdurate" past will jeopardize her safety, but reluctantly changes his mind after she convinces him that he will fail without her assistance.
Split into simpler sentences: When Sadie offers to help, Jake initially refuses, fearing that the "obdurate" past will jeopardize her safety. However, Jake changes his mind after Sadie convinces him that he will fail without her assistance.