iMessage doesn't say "delivered"
If your friend turned off iMessage or turned off Read Receipts, then you won't get the Read notification.  If they're using a beta of iOS 10, they can turn off Read Receipts for individual contacts.

Also, as you suggested, if the friend decided to block you, you won't see the notifications, either. 

EDIT: As indicated in the comments, you will see the Delivered notification even if Read Receipts has been turned off.  Edited answer to reflect that.