I didn't read it that way at all, Amane was happy he'd be cosplaying that character, and Ijichi was proud of him for talking to someone on his own initiative, I saw both of them as 'way to go' play punches.
You're free to infer this scene that way since there was nothing explicit, but these are the reasons I assumed jealousy.
Amane was the type that wants to cosplay herself. That's why she was disappointed that she couldn't wear bunny suit or headpiece. She was also worried that her otaku ness would get exposed.
Yet MC has no such barrier.
If she was excited for his cosplay, the previous panel would have her be more excited.
Edit: in a later
chapter, it was more explicitly mentioned that she was envious.
Edit 2: heck, I just realized that even the subchapter 86 is titled "jealous"
For Ijichi, the other girl said that she'd be annoyed if her bf excitedly talked to another girl.
The point of this scene was that she argued her interest is like a parent, but in reality her interest is like a gf type.
And "way to go" punch is usually one punch, not multiple.