would anyone kindly help me understand why everybody is sad as fuck in this manga right now?
Cliff Notes version:
During Komiket, the Haniel cosplay went viral and Marin was swamped by fans taking pictures, but Gojo suddenly felt like Marin was out of reach from him and it depressed him.
Marin's Dad shows up and further complicates things by making Gojo think he's happy that he takes care of Marin like a housekeeper. Finally the two of them get together and talk. Gojo tells her that he's grateful that her cosplay has helped his training but he wants to accomplish his dream of achieving the level of Hina Doll Craftsman before Gramps shuffles off his mortal coil, which makes Marin think that her cosplay requests have cost him precious time for learning the craft.
As she's pondering this, a call from his cousin further destroys the mood as she tells him that Non-Chan, the girl who broke little Gojo all those years ago by telling him she hates him, has come to visit. And she's standing there in front of the store waiting for him.
Then we get a flashback to when Gojo first lost his parents. He first lived with his cousin's family, but was too depressed to do anything except roll himself up in his futon. Non-Chan would come over and read to him, trying to cheer him up, but a while after, Gramps brought him to the Hina Doll store and it awakened his desire to follow in Gramps's footsteps. About a week before he went to live with Gramps as his apprentice, Non-Chan learned that he was moving, and it was clear that she liked him, but now, Gojo was fixated on making Hina Dolls and she exploded, calling him weird and saying that she hated him, breaking his artistic heart, and making him the timid introvert we met at the start of the series.