How to Find Out If Someone Unfollowed Me on Tumblr
Tumblr's microblogging platform is specifically designed with social integration in mind, which means that you receive notifications when new users on Tumblr start following your blog. However, Tumblr does not notify you when someone unfollows your blog. If you have only a few followers, it's easy to consult the list of people on your "Followers" page and look for a specific user, but if you have many followers, use the "look up follower" feature to see if the person is still there.
Navigate to Tumblr.com and log in to your account.
Click the "Followers" link in the right column of your Dashboard.
Type the name of the Tumblr user you want to check into the "Look up follower" form in the top-right corner of the page.
Press the "Enter" key. If the user's name appears in your search, he did not unfollow you. If Tumblr displays a "This user is not following you" message, that means the user is no longer following you.