I think gojo angry with himself for thinking like in the past chapter. He's silent because he's in the middle lf intropecting. And Marin thought Gojo us mad at her
I feel like he is deep into the character Marin is cosplaying. He really put importance into his craft, he painstakingly made the cosplay and Marin is doing her best to incarnate into the character, this nonhuman being, and Gojo is in contemplation of what they accomplished.
Gojo may have feelings for Marin, but to me his work takes a big place in his life, so I don't think Gojo is angry/depressed/jealous of Marin, not related to romance at all, but it is Gojo simply thinking of furthering his craft.