Be compatible and friendly (3,2,3)
I believe the answer is:
hit it off
'be compatible and friendly' is the definition.
This is all the clue.
(Other definitions for hit it off that I've seen before include "Become immediate friends" , "Develop a good friendly relationship" , "Get on well - with a blow?" , "Become compatible and friendly" , "Agree - get on well together" .)