Co-tenant is depressed by ecstasy under the carpet (8)
I believe the answer is:
flatmate
'co-tenant' is the definition.
I can't judge whether this defines the answer.
'depressed by ecstasy under the carpet' is the wordplay.
'depressed by' becomes 'flat' (I am not sure about this - if you are sure you should believe this answer much more).
'ecstasy' becomes 'E' (informal term for the drug).
'under' says to put letters next to each other (in a down clue, some letters go below others).
'the carpet' becomes 'mat' (a mat is a floor covering).
'e' after 'mat' is 'mate'.
'flat'+'mate'='FLATMATE'
'is' is the link.
Can you help me to learn more?
(Other definitions for flatmate that I've seen before include "Person sharing apartment" , "I may share with someone" , "Cohabitee" , "in the rooms one shares" , "one sharing same pad" .)