Bring love into it, which is tedious (6)
I believe the answer is:
Here is my best explanation:
'is tedious' is the definition.
('boring' can be a synonym of 'tedious')
'bring love into it' is the wordplay.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'into it' is an insertion indicator.
'bring' enclosing 'o' is 'BORING'.
'which' acts as a link.
(Other definitions for boring that I've seen before include "Tedious and tiring", "Tedious, tiresome", "Tedious, of no interest", "Drilling - it's monotonous", "flat", "Making holes", "like watching paint dry?", "dull", "Mentally wearying" and "Dull and repetitive, a turn-off".)