He teaches less than the truth, perhaps, about love (5)
I believe the answer is:
tutor
'he teaches' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'less than the truth perhaps about love' is the wordplay.
'less than' means to remove the last letter (not the full word).
'perhaps' indicates an anagram.
'about' indicates putting letters inside.
'love' becomes 'o' (love means zero in tennis).
'truth' with its final letter taken off is 'trut'.
'trut' is an anagram of 'tutr'.
'tutr' enclosing 'o' is 'TUTOR'.
Can you help me to learn more?
(Other definitions for tutor that I've seen before include "Private educator" , "Mentor" , "Edify" , "college teacher" , "Give individual instruction" .)