This is one of the cruelest portraits on loneliness I've ever seen. The main characters in Kechiche's previous films, Krimo in L'Esquive and Slimane in La Graine et le Mulet, despite their introverted nature, never feel as isolated as Adèle. They are always surrounded by their family and friends, for better or worse. It's probably why Kechiche didn't bother to develop any of the ancillary characters here like he used to do.
To think of how much the idea of predestination define Adèle makes the final scene absolutely devastating. Her romance with Emma both begins and ends with it, love at first sight eventually cannot escape the social class division. She never fit in with Emma's artist's circle, but she also can't find happiness if she settles for someone less. No matter how sexually compatible they are, everything else comes before the carnal desire for their relationship to be sustainable. Stuck in limbo makes Adèle so alone in this world.