Could It’s Not Fair possibly be about Mark Ronson?
As far as I know, they were never romantically linked in the press. However, I don’t see Lily playing her music for an ex who she ended on bad terms with. Who would she play her a track she wrote with Greg Kurstin for? Mark, for one. If she played the track for him, he might have thought it was just for artistic feedback. If she played it for a non-collaborator ex with no business reviewing her work, that ex might cop on to the criticism more easily with no professional pretense.
And, Lily has said they’re extremely close. He’s considered quite handsome and a bit vain, so he might able to get away with being a low-effort lover and not realize it.