If you're having trouble seeing someone's stories on Snapchat, it's likely because they have not added you as a friend or they have blocked you. If you think this is the case, you can try reaching out to them through another medium (like texting or Facebook) to see if they'll add you back so that you can view their stories. Additionally, check to see if your account is set to private in your settings. If it is, only people who have added you as a friend will be able to see your stories.