Things former pupil lost in binges (8)
I believe the answer is:
sessions
'binges' is the definition.
(eg a session of drinking)
'things former pupil lost' is the wordplay.
'things' becomes 'obsessions' (as in having a 'thing' for someone).
'former pupil' becomes 'OB' (abbreviation for 'Old Boy').
'lost' is a deletion indicator.
'obsessions' with 'ob' removed is 'SESSIONS'.
'in' is the link.
(Other definitions for sessions that I've seen before include "Sittings, terms" , "Meetings, of court perhaps" , "meetings or series of meetings" , "Meeting periods" , "Comedian" .)