Basically, Izuku was engaged to Katsuki and about six months before their wedding Katsuki got a mission, even though he was supposed to be off. This one was apparently really, really important but also really really classified. Katsuki told Izuku he’d be back within the month and Izuku believed him, but the mission was zero contact so Izuku wouldn’t know exactly when he’d be back till once he got back. But a month passed and Izuku hadn’t heard or seen Katsuki and then the hero commission showed up and they told told Izuku that Katsuki died. They said there was no body. Izuku screamed, he cried, he lived in denial. Izuku lived through the funeral. And eventually Izuku went back to his life because he had to move on because he had people who depended on him. But he wasn’t the same. Katsuki was Izuku’s whole life. He was Izuku’s everything. And now Katsuki was just… gone. So at first Izuku started drinking, but he couldn’t do that and go to work and he was trying not to show anyone he was falling apart. So Izuku stopped drinking, except for when he was at a reunion or something the normal amount people would drink. But Izuku started smoking a lot and he hid it from everyone and he knew Katsuki would kill him if he ever had seen him smoking a cigarette, but Katsuki wasn’t here to do that anymore.