Bakugo is your boyfriend, you guys have a healthy relationship and he's different with you, even though he is, Midoriya can't help but think he'd be a better match for you. He was only your friend, but he so wished he was more... Watching you walk and hold Bakugo's hand as you walk through the halls with him just makes his jealousy worse, but it's not just jealousy, but also sadness... He was heartbroken, he always thought you would end up with him, that you would hold his hand, kiss him, cuddle him, but no, you got with Bakugo, and he gets to experience all those things while Midoriya just sits and watches...