My theory is that Gojo negative expression in this chapter is less about his relationship with Marin and more about his competence as an artisan. I would expect that an artisan would want their pieces to be appreciated by it's own merit and not through the endorsement of others. In other words, the dressmaker would want their dress to loved because it good and not because the model makes it look good.
In chapter 99, Gojo regretted telling Marin to make people fall in love with her. Perhaps Gojo is feeling this way because he's entirely relying on her to make cosplay work. We've established Gojo has self esteem issues, so maybe these negative emotions are because he feels like he isn't doing enough to support Marin. The wall of people intentionally misleads the reader to think that it's a wall between Marin and him, but another way to look at is it's people who isn't looking at Gojo. People who look are looking at Marin and not at the work he's done.
As mentioned in this chapter, the cosplay only worked due to the culmination of both Gojo's and Marin's efforts, but Gojo doesn't see it that way.
In chapter 96, he clearly stated that the dress isn't up to par and that he is relying on Marin to make it work. He also said something about making people falling in love with Haniel's costume the same way he fell in love when he saw a Hina doll for the first time. This further supports the idea that, as an artisan, he wanted people to fall in love with the costume, but he decided to rely on his crutch of Marin making it work.
Relying on her too much to make his work succeed is making him feel like he's giving up as an artisan, and that's what causing him to regret his words.
