Lyric discussion by AwesomeKing 

Cover art for Not in Love lyrics by Crystal Castles

I think the song means that he was in a great relationship and for whatever reason it was over and he is trying to convince himself or to both of them that they are not in love anymore. Although he probably would love to hang on to the greatest memories and keep thinking there is something there but sure enough there is not.

My Opinion

that's what i got out of it too.