Harry found out about soulmates when he first arrived at hogwarts, seeing Hermione meet hers, a girl named Lavender, and seeing Neville and Hannah show each other their soul marks on the train. He had always wondered about the markings on his thigh, but his curiosity always made him get more chores from petunia so he always held back his questions. Apparently in the Wizarding world it was common to have a soulmate, many people being brought up with the idea of someone waiting for them, their other half. Sure, Harry had heard the fantasys muggle girls would have about meeting their soulmate, but he had never believed them to be true, just a wives tale. He eventually found out about them when Ron saw his as he was changing into his robes, proceeding to tell him everything about them. His older brothers had yet to find theirs, other than Percy who found his in his third year. His sister Ginny had found hers when she was young, playing with a friend. Apparently they never knew it until they were both eight. Ron had yet to find his, but he held hope that he would find his other half soon. His words were scribbled in condensed handwriting around his upper thigh, being easy enough to hide beneath shorts, and now robes. The words were simply 'you don't have to do this' which, if he was being completely honest, scared him. It was such a vague statement, but st least he didn't have the words 'You must be a Weasley' like Ron did.
Harry went through his entire time at hogwarts seeing his friends pair off and spend most of their time with their soulmate. It wasn't the first time Harry felt like he was alone in the world, and it probably wouldn't be the last. Harry had grown up feeling alone and seperated from his peers and family, so to say he was used to the feeling would an understatement. Dudley always sought to make him an outcast, and now he was, in both the muggle world and the Wizarding world. Although being hailed a hero, Harry didn't make that good of friends. Sure, he had Ron and Hermione, but both of them were occupied with their soulmates and Harry didn't want to intrude on them and their soulmates. They helped him with things and he helped them, it was simple, but still harry felt more alone than ever.
Harry feeling alone for most of his hogwarts life made it surprising when Ron and Hermione left their soulmates at Hogwarts and followed him on his hunt for horcruxes. He returned back to Hogwarts and found everyone gathered, he found Snape dying, and went to go watch the memories when he heard the message of the short break and the reasoning behind it. He watched the memories and realized what he had to do. His body turned numb as he walked through the halls in search of his friends. He finally found them in the main hallway, where he told them what he was doing. He was so preoccupied with the thought of him dying at seventeen, he didn't even notice Nott coming up behind him. Didn't notice him until he felt a tap on his shoulder, and Harry swore that he must of jumped a mile high.
"You don't have to do this Potter" Nott's oddly panicked voice said as Harry turned around.
"Someone has to win this war, Nott." Harry sighed, barely even registering the burning sensation on his thigh. He did, however, register the chaste kiss that Nott gave him that had them both blushing scarlet.
"Try not to die, okay?" Nott tried to smile at him but it came out grim and shaky.
"I'll try." Harry's tongue felt like lead as he told hint he blatant lie. In a moment of pure adrenaline and desperation, Harry pulled Nott into a deep kiss, his hands clutching his chirt Nott's hands on his cheeks. "Just in case" Harry murmured as he broke off from the kiss. He took a deep breath, and hugged both of his friends, and gave all three of the people he cared about a smile and a nod as he walked off to his certain death.
Theo joined Hermione and Ron when he walked out onto the courtyard. He made small talk, telling them things about him, talking about why he had never talked to Harry before then. His mind was elsewhere, praying to any gods out there that his soulmate would return to him safely. So, when he saw Harry's limp body being carried by their caretaker, he almost started crying. Fate was a cold bitch, his father always told him after complaining about his mother. No matter how much he hated his father, he couldn't help but agree for once. He didn't cry, but the sound that came out of his mouth sounded like he did as he lifted his hand to cover his mouth, watching as Neville stood up to you-know-who. The boy didn't know what he was up against. Although his speech was inspiring, his following actions were pretty cool. Or at least they would have been had Theo been paying any attention to Neville. He was paying attention to Harry, and this time he did sob as Harry jumped out of the giant's arms. Suddenly the battle was back on, everyone was fighting and from the corner of his eye he could see death esters being taken down. Fenrir, Bellatrix, Dolohov, and finally Voldemort, all fell. After their leader fell, their forces retreated, and Theo hoped that they would find themselves in Azkaban soon, for good this time. When he saw Harry alone in a hallway off of the Great hall, he didn't hesitate to yell his name and practically jump into his arms. Harry's hands wrapped around his back and his own were twined around his neck, playing with his hair. They both just held each other for a few minutes, Theo's head on Harry's shoulder, reminding himself that Harry was here and very much alive. Theo moved his head up to place a gentle kiss on the taller boy's mouth, causing Harry to smile a little bit despite the grim circumstances. "Next time you decide to sacrifice yourself to an evil wizard, at least tell me what your plan is first."
"What, afraid you were gonna lose me?" Harry got a bit cocky and smirked at him, turning him so his back was towards a wall.
"Always" Theo answered him honestly.
"Well," Harry said, pushing him up against the wall behind him. "I'm not going anywhere." Harry's lips descended on his neck and Theo decided that maybe it was worth the scare. He had his other half, that's all that mattered.