Always forgetting where Lebanon is, assuming Norway initially in Middle East (7)
I believe the answer is:
amnesia
'always forgetting' is the definition.
'where lebanon is assuming norway initially in middle east' is the wordplay.
'where lebanon is' becomes 'asia'.
'assuming' indicates putting letters inside.
'initially' indicates taking the first letters.
'in' means one lot of letters goes inside another.
'middle east' becomes 'me'.
The first letter of 'norway' is 'n'.
'n' inserted inside 'me' is 'mne'.
'asia' going around 'mne' is 'AMNESIA'.
(Other definitions for amnesia that I've seen before include "Asia men with memory loss (7)" , "Mental condition" , "As a mine (anag)" , "Defect in memory" , "Pathological forgetfulness" .)