You can unfriend this way:
Go to "Community" on top right of page.
Under "Community" choose "My Language Partners."
When you see your list of "My friends" go to the entry for the person you want to unfriend. You will see two symbols on the right: "talking bubble" and "three dot bubble." The two symbols appear on the right of each friend entry.
Left click on "three dot bubble." You will see three choices. The third choice is "Remove from this list."
Click on "Remove from this list."
Now the person should be removed from your friend list.
This works on the computer. I don't know if it works on the app on a cell phone. Good luck!