Really loving (4)
I believe the answer is:
into
'really loving' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for into that I've seen before include "Teachers' trade union" , "Not I (anag.)" , "Keenly interested in" , "Taking a lively and active interest in (colloq.)" , "To a position within" .)