Perhaps they want to cut off all forms of connection with you. By blocking you from seeing their stories, they're trying to create more distance in the aftermath of the breakup.
Maybe the file format of your story is not compatible with the loading system. Check if it meets the required format specifications. Another possibility is that there's a server issue on the hosting side. You could wait for a while and try again later.
One possibility is that your story doesn't meet the platform's content guidelines. Another reason could be that the upload process has some technical glitches on the server side. Try again later or contact the support team for assistance.