Happiest saddest day why?

Sister and besty are the same in that whenever it's a good day wonderful day and we had lots of fun. By the afternoon they are depressed and angry and sad.

Kinda have up trying to have good days with them cause they just end up being miserable to be with.

What causes this? It happens when they are apart also so it's not just one of them being weird sad and depressed after a good day

Happiest saddest day why?
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