Threesome without end relating in complex way? (7,8)
I believe the answer is:
eternal triangle
'threesome' is the definition.
(eternal triangle can mean a love triangle)
'without end relating in complex way?' is the wordplay.
'without end' becomes 'eternal' (I've seen this in another clue).
'in complex way?' indicates an anagram (I've seen 'in complex way' mean this).
'relating' anagrammed gives 'triangle'.
'eternal'+'triangle'='ETERNAL TRIANGLE'
(Other definitions for eternal triangle that I've seen before include "Complex relationship" , "In which three lovers" , "sexual relationship" , "Love relationship between three people" , "emotional relationship" .)