The boy could react in different ways. At first, he may be shy and keep to himself. But as the girls start having fun, he might loosen up and start laughing along with them. He might also feel a bit awkward when they start talking about girl - stuff like crushes, but he could still be polite and listen.
Writing sexual fanfic, especially when it involves non - consensual or inappropriate use of characters, is not appropriate. It goes against ethical and respectful creation of fan - made content.
I don't know exactly. It could depend on the specific manga universe or storyline. Maybe you can search through popular manga forums or fan communities for the answer.
They have a complex and somewhat ambiguous relationship. It's not straightforward love but a deep connection based on mutual understanding and shared experiences.