"It's okay to be afraid, angel." Crowley replies, assuming a bit that fear was the major cause for such morbidity. "Just don't give up on me." 

Crowley isn't sure where to go from here. He knows Aziraphale isn't ready to give up, that much is apparent, but he also knows that coming to terms with their own mortality is in itself terrifying, and Crowley counts his blessings that he hasn't had many swipes with death yet.