Harry Potter:
Harry would immediately reassure you that you had nothing to worry about, putting a comforting arm around you and kissing your forehead. You'd immediately feel stupid for ever feeling jealous, since Harry was really good at making you remember he only wanted you. He cared for you deeply, and there was nothing he could ever do to ruin your trust. It was just nice to have that as a reminder whenever the few times came around when you forgot.
Ron Weasley:
Ron was beyond surprised to hear that you were the one jealous of him. He blinked at you for a few seconds after you told him, attempting to process the news and decide how to react. You almost regret telling him how you felt, considering he walked around with his shoulders back and a little proud of himself that he means that much to you. He had gotten quite used to always being the jealous one; it was nice and different for him to not always be the one dressed in green.
Draco Malfoy:
Draco would quirk a brow with a smirk on his face, intently watching you as you rambled about how the group of girls in the year below you always seemed to follow him around and try to catch his attention at meal times. After complaining to him for a solid five minutes, you'd eventually catch him trying to hold back his laughter. When you asked him 'what', he would just shrug and refuse to reply, finding your jealousy wildly amusing since it's very rare for you to ever show any sort of negative emotion.
Fred Weasley:
Fred would find your jealousy quite funny, playing into your delusion. You'd be shocked to hear him complimenting the person you were admitting to be jealous of. Your jaw would drop, but Fred would only be able to keep up the joke for a few seconds before he'd start laughing. He'd immediately start reassuring you that you didn't need to be jealous and that he only had eyes for you. While you didn't like his initial reaction to your jealousy, you knew that his sweet talk afterwards was enough to make you breathe easy once again.
George Weasley:
When George could feel you about to go on a jealous rant, he would immediately try to stop you from talking in a way that was bound to make you laugh. He'd say 'zip' or put a hand over your mouth, telling you that you weren't being rational and that he had eyes for only you. Of course, you'd be laughing so much and trying to swat him away so much that you would forget what you were talking about, instead turning all of your attention on George and trying to get him back.
Neville Longbottom:
Neville doesn't quite pick up the hints that you were jealous when you saw him spending time with Luna. You would constantly bring her up, trying to question the nature of their relationship and figure out what he truly thought of her. Of course, he would innocently answer, only thinking of her as a friend. Eventually, he'd share this information back with Luna, and she'd laugh, telling him that you sounded jealous. It would take him a while to believe the idea, but eventually, he'd realize that it was true.
Cedric Diggory:
Cedric thinks it's adorable that you're jealous, being sure to tease you about it when you were venting to him. You would playfully shove him, denying your jealousy as he continued to kiss your cheeks and shower you in affection. He would do whatever he could so you wouldn't have to worry about him, and your jealousy would immediately dissipate into nothing.
Newt Scamander:
Newt is unbothered by your jealousy, knowing that there was no need for it. While you wanted to continue to ask him questions about the girl who seemed to be interested in him, he would mostly just shrug it off and refuse to talk about it. Of course, that opened up a conversation between the two of you where you talked about your relationship and how you felt about jealousy.
Sebastian Sallow:
Sebastian would never admit to it, but he kind of liked the fact that you were jealous. While he sat next to his class partner (the girl you were jealous of), he was now aware that you were probably quietly seething behind them. He would never do anything to try and make you more jealous, keeping his distance more. Though there would be a soft smile on his face all class, especially when he turned around and saw your annoyed expression looking directly at the two of them.
Ominis Gaunt:
Ominis would take the opportunity to tell you that you have nothing to worry about, though he would do so rather coldly. He'd state all the reasons as to why your jealousy was irrational and you didn't have to worry. It would take you a while to recover from the blow, Ominis not realizing that you felt embarrassed and sad. Eventually, he'd pull you into an embrace, hugging you and making you feel safe again.
Garreth Weasley:
Garreth would take it to the extreme and completely avoid the people who were making you jealous. While you didn't want him to cut off his friends (especially the girls that seemed like they had a crush on him), you told him that your jealousy is something you have to work through on your own and not something that he had to change about himself. He wanted to make sure you were always happy and realized that cutting off his friends was not the way to do it.