Parents
At Justine’s wedding party, some guests start to give their speeches. Her father is also suddenly asked to give a speech which leads to a display of Justine’s father and mother confronting each other and her mother highlighting the hatred she feels for marriages. At the moment, Justine’s parents symbolize the fears that she starts to feel within herself. She starts to fear that she might be headed in the same direction as her parents.
Justine and Claire
The first half of the movie is titled "Justine." And during that half, the movie focuses on Justine and makes her the protagonist of our story. We see her depression taking over her. Her whole character symbolizes the illness called major depressive disorder (MDD). The second part of the movie is titled "Claire." And during this part, we see a lot more screen time for Claire. We see her anxiety and her overall behavior reflecting the illness called generalized anxiety disorder (GAD).
Melancholia
The planet that the film shows is about to collide with Earth is aptly named Melancholia. The planet itself symbolizes many aspects of the film. It symbolizes Justine’s depression. As the planet draws in closer the more depressed and detached Justine seems. It also symbolizes Claire’s rising anxiety towards the issues her sister is facing and she, in general, is facing.
Future
During Justine’s wedding, her husband Michael keeps trying to take hold of Justine and tries to comfort her. At one point, Michael shows Justine a photo of land he purchased which is meant to be their future home. He gives it to Justine who reluctantly takes it. This photo symbolizes the future Justine could have had. But later on, when everyone is dancing, we see the photo in her lap and she stands up leaving the photo to fall on the floor behind her, leaving the promised future of happiness behind.