Since some readers will have MCs who don't attend the same school/class, this is basically how another classmate found out the MC and their lover are together.

Izuku Midoriya:

He didn't expect you to appear when you entered the class and approached him, holding his notebook to him, telling him he forgot it and you know how special he finds it so you thought he would need it. His face went bright red as he could feel the whole class staring, stuttering out a thank you as he took the notebook, shyly whispering you didn't have to. When you left, half the class was surrounding him, asking him thousand of questions about you and how you both met and so on.

Katsuki Bakugo:

You were waiting for Bakugo at the school gate when this tiny dude with purple balls as hair began badly flirting with you. Before you could tell the dude to get lost because he's making you uncomfortable, a foot kicked slammed against the kid's face causing him to fall. Bakugo angrily yelled why the fuck he's flirting with his lover before he took your arm and dragged you away. The next day, the whole class knew because of Mineta, who was jealous of Bakugo for having gotten a lover while he hasn't, that Bakugo has a lover and who they are.

Shoto Todoroki:

He forgot his backpack at home. He was unsure what to do, whether he should borrow something from a classmate or go home to get it, only to stare as you walk over, giving him a wave while holding his backpack up to tell him you are here to give it to him. As you gave it to him, he thanked you before saying you shouldn't have done this because now you have to hurry or else you will be late. When you left, Momo and Urakaka approached him, asking who that was. Shoto calmly told them that he's dating you and you came to deliver his backpack. When the two gave him a shocked expression, whispering they never expected him to get someone, he just blinked, unsure what to think of that before he walked to class.

Ochaco Uraraka:

She was excitedly talking to you, only to let out a shocked yelp when someone ribbited out her name. She twirled around to see Tsuyu causing her face to turn red, stuttering out Tsuyu's name, who told her to call her Tsu. She nervously asked Tsuyu why she's here, not having expected this and not having gotten time to prepare to introduce you to her friends. When Tsuyu looked at you, Ochaco blushed as she held her hand to you, saying who you are, stuttering out you are her lover before she told you that this is Tsuyu, one of her friends from school. After Ochacho calmed down, you all had a nice conversation before Tsuyu left. Ochaco sighed, putting her hands on her cheek to feel how hot they are because her face feels very heated, mumbling she wasn't prepared for that.

Tenya Iida:

He was rambling to you about something when you pointed behind him, telling him you think two people are spying on you both. Tenya was quick to freeze before slowly looking over his shoulder, expecting to see an enemy, only to stare at Deku and Ochaco, who were peeking around the corner of a street. He stared before he sighed, assuring you it's okay and they are his friends. He knew they would keep spying so he turned, telling them he knows they are there. Deku and Ochaco awkwardly looked at each other before coming out of hiding, Ochaco being first to apologize, assuring Tenya they didn't mean to but it was such a weird sight and they wanted to be sure you two were together so they don't make fools of themselves when they bring it up next time. Tenya forgave them, but not after giving them a scolding. Once he was done, Ochaco excitedly greeted you, introducing herself and Deku, who nervously and shyly waved, saying she hopes you can all be great friends.

Eijiro Kirishima:

He was following Bakugo, trying to convince him to come over to his place to play video games, when he suddenly spotted you so he froze before he shook Bakugo, who angrily asked him what the hell he's doing. Eijiro pointed at you, saying that's his lover. Bakugo glanced at you before giving Eijiro a "why should I care?" look so Eijiro slouched on him, mumbling he's so happy he got you as his lover, only to yell in shock when Bakugo shrugged him off and stormed away. Eijirio just laughed it off before he jogged to you, happily shouting your name to get your attention.

Tsuyu Asui:

She and you were walking through the city when Tsuyu heard her name being called so she turned to see all the girls from the class making her ask why they are all out. Ochaco said they are having a girl's day, telling her they send her messages but she never replied. Tsuyu pulled out her phone to see all the messages she got so she apologized, saying she had her phone on silent because she's on a date with you. When she saw the shocked expression of the girls, she just calmly introduced you to them. When you told Tsuyu she should hang out with her friends, Jiro was quick to shake her hands, assuring you that they wouldn't wish to disturb your date before she pushed the girls away, nervously telling you both to act as if this never happened and continue your date.

Momo Yaoyorozu:

You and her were out shopping. She needed some books to further her knowledge so she can create more. As she was scanning the books, she heard a familiar voice call her name so she looked to see Jiro. Momo gave her a smile, greeting her before curiously asking why she's here. Jiro held up a guitar case, saying she needed a new case before she fell silent, staring at you causing Momo to blush before she introduced you two to each other. Jiro awkwardly nod, not having expected this but then smiled and teasingly said she will leave you two to your date before she left, leaving Momo to stutter out that this isn't a date. She covered her face, feeling embarrassed before she apologized to you, saying first she drags you with her to this shop and now her friend teased you.

Denki Kaminari:

He was walking with Jiro from a music store, just chatting, only for Jiro to yelp and get confused when he suddenly hid behind her. She looked over her shoulder to see him trying to fix his hair, nervously asking if he looks good. Jiro was confused as she said he looks as he always looks. Denki got up, ready to approach you as you both made eye contact, only to realize him walking with a girl might look as if he's cheating so he was quick to point at Jiro and yell she's his friend and they are not dating, to which Jiro was wondering if he's finally losing it. When you laughed and assured him you know and trust him to never cheat, he smiled like a dork before he blushed and decided he should probably properly introduce Jiro to you now.

Kyoka Jiro:

She was walking from school with Momo when she saw you. When you approached, she felt her face heat up as she awkwardly asked you why you're here. When you told her you came to pick her up, she gave you a confused expression so you held up your phone, showing the messages you both send, agreeing to meet after school to go get some drinks at a cafe. She gasped, saying she's so sorry and she forgot. She awkwardly looked at Momo, who smiled and assured her she can go and she will walk home alone. Kyoka felt bad so she glanced at you with a question look that asked if Momo can come along so you shrugged so Kyoka gave Momo a smile, telling her it's fine with the two of you for her to come along, and then she and you can get to know each other since she would like it if her lover and her friend can also become friends.

Fumikage Tokoyami:

He was at a cafe with you, having a nice time talking to you, when he heard someone gasp so he looked to see Ashido. He was confused but then his face turned red as he realizes he got caught on a date so he looked away, trying to hide his flustered face as he asked with a stutter what she's doing here. Ashido told him quickly she wanted a drink before holding her hand to you, excitedly saying she's Mina Ashido, asking you who you are, asking if you are Tokoyami's lover. When she left, she had already texted all the girls this exciting news she just discovered.

Mina Ashido:

She was teasing Ochaco for having a crush when she spot you so she told her if she loves someone she should go for it before she loses the chance. She waved you over so you walked over. She excitedly put her arm around your waist, telling Ochaco that she went for it and that's how she ended up having this cute, beautiful person as her lover. Ochaco seemed shocked so Mina couldn't help but laugh before she told you that this is Ochaco, a friend of hers who is having trouble with her love life. So the rest of the day was spend giving Ochaco love advice and telling her fun things you and Mina have done together as a couple that she should try when she gets a lover.

Yuga Aoyama:

When he saw Todoroki while you and him were shopping, he was more than proud to brag about his lover to him. Todoroki was just confused and stared at him, wondering when he can go home. When Yuga laughed out he can go, Todoroki wished you a farewell before he left. When you said Todoroki didn't seem impressed, Yuga laughed out that's how he always is.

Eri:

When she was out, walking with Aizawa, she saw you so she excitedly tugged his hand, pointing at you, saying she wants to go greet you. Aizawa looked at you, making sure you are a safe person to hang out with Eri before he walked to you so Eri can greet you and have some fun talking to you. Eri was happy, and a bit shy, to introduce you to Aizawa.

These take long to write since I have to write three chapters/for 22 characters so sorry when updates take a while.