More than a couple get amnesia or worse (6,1,5)
I believe the answer is:
menage a trois
'more than a couple' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'get amnesia or worse' is the wordplay.
'worse' indicates an anagram (I've seen this in other clues).
'get'+'amnesia'+'or'='getamnesiaor'
'getamnesiaor' with letters rearranged gives 'MENAGE A TROIS'.
Can you help me to learn more?
(Other definitions for menage a trois that I've seen before include "household of unusual size" , "complicated arrangement!" , "Triangular relationship(s)" , "living arrangements" , "third party involvement?" .)