Natsu might be initially shocked and confused. He's not the type to expect rejection, so he could be at a loss for words at first. For instance, he might just stand there with his mouth open, not believing what he just heard.
Well, in many fanfictions, Natsu might initially be in shock. He's a passionate character, so he could react with anger. He might lash out at Lisanna or the person she cheated with. He could also go into a state of self - doubt, wondering what he did wrong.
She might become angry at first. Natsu is known for her fiery temper. So, she could lash out at the person who betrayed her, confronting them directly and demanding an explanation.
He may try to understand Erza's reasons. Natsu, despite his impulsive nature, has a big heart. He might respect Erza's decision and step back, trying to keep their friendship intact. However, he could also be a bit persistent in a non - annoying way. He might keep showing his care for her in a more friendly manner, hoping that over time, she might change her mind.
Well, Natsu is a passionate character. He could react with a lot of excitement. He might pick Lucy up and spin her around, laughing and saying how amazing this is. Or, he could also get a bit worried and start asking Lucy all sorts of questions about her health and what they need to do next.
Gray would be extremely angry. He would immediately start looking for clues as to where Natsu was taken. His ice - make magic would be on full display as he might freeze things in frustration while trying to figure out the situation.
Natsu's friends would have a range of reactions. Lucy would be distraught, her face pale with fear as she kneels beside Natsu. Gray would clench his fists, his eyes filled with rage as he scans the area for the shooter. Erza would be the voice of calm and reason, though her hands would be shaking slightly as she tries to stop the bleeding. Happy would be flying around in a frenzy, screeching in distress. They would all be united in their determination to save Natsu and seek justice for what has happened.
His close friends like Lucy would be extremely happy. They might cry tears of joy and immediately hug him. Gray, on the other hand, might act cool at first but then show his true happiness. Erza would probably be the most composed but still show her delight through a warm smile.