Admit being depressed losing diamonds (3)
I believe the answer is:
own
'admit' is the definition.
(thesaurus)
'depressed losing diamonds' is the wordplay.
'depressed' becomes 'down' ('down' can be a synonym of 'depressed').
'losing' indicates named letters should be taken away.
'diamonds' becomes 'd' (abbreviation in bridge say).
'down' with 'd' removed is 'OWN'.
'being' is the link.
(Other definitions for own that I've seen before include "Have in one's possession" , "Personal; possess" , "Possess - recognise - admit" , "Private" , "Acknowledge" .)