It wasn’t until the shift after a chimney collapsed on Severide that Kelly found out exactly what happened during his rescue.
Towards the end of being trapped everything had started to go a little foggy, the only constants being Matt’s increasingly strained voice and the suffocating heat and the smoke crowding his lungs. He didn’t remember being dragged from under the chimney or being all but carried down the stairs. He was in the burning house, and suddenly he was sitting outside on the grass trying to breathe while everyone else cleaned up and shot him concerned looks every few seconds.
(He remembers Matt’s gaze burning into his, blue eyes bright with worry, how he deflated with a shaky laugh when Kelly shot him an unsteady thumbs up before looking away, even though Kelly couldn’t tear his gaze away, could never tear his gaze away-)
Severide was walking past the squad table late into the night, where his men and most of truck were crowded around while Cruz regaled them with the story of Severide's rescue, everyone too caught up in the story to notice that the Lieutenant was striding by. Morbidly curious, Severide stopped reading the forms he had been scanning and focused on Cruz's animated voice.
"-But time was running out, and of course Casey was going to stay and try to shield Severide with his body and get them both-"
Severide slowed without meaning too, unable to catch the rest of the conversation through the sudden roaring in his ears, unable to think past the sudden lurching of his stomach.
"Casey was going to what?"
The story came to an abrupt halt as all eyes whipped towards the fiery Lieutenant.
"Casey..." Cruz trailed off, and Severide had no idea what expression was on his face but Cruz's eyes were wide and more than a little nervous. "I thought- you were conscious."
Severide inhaled sharply, biting the inside of his cheek to keep from snapping something that he would regret.
"Barely," He said flatly, and Cruz and Otis both flinched slightly. "Casey was going to stay?"
"He ordered me to leave. It wasn't looking good, towards the end" Cruz said after a long moment, "but he...he said he was going to stay so that you could both make a stand. He-"
He was going to stay and die with Severide, in other words, and suddenly Kelly was back in that flaming house, trapped under a giant fucking chimney and he couldn't breathe-
(And he wasn't thinking about the time that Boden had forced him to see a therapist, some too bright young man who had never set foot near a dangerous situation in his life, who had asked casually what came to mind when Severide thought of the word "safety" and Kelly had automatically said "Matt" and proceeded to never go back, he wasn't).
Severide ignored whatever else Cruz had to say and blindly strode past the table and into the common room, gaze instantly locking onto Casey, who was sitting at one of the tables talking to Brett, eyes bright with amusement and the beginnings of a smile curving across his face.
"Captain, a word?" His voice was tight and a little too loud, and Casey's eyes jolted to his, widening in surprise. Before he was given a chance to respond Severide had grabbed his arm and all but dragged him out of his seat. He didn’t let go or look back until they were outside, and he knew that it was completely psychotic, grabbing Casey like this and dragging them both into the cold and snow, but at that moment he couldn’t care less.
When he finally whirled around to face Casey, the other man looked confused and defensive and more than a little wary, "Severide, what's-"
"You were going to stay."
Casey’s brow furrowed. "Stay-"
"In the house," he had to fight to keep his voice from shaking, "With me, when the chimney collapsed, you were going to stay.”
Casey stared at him for a moment, face unreadable, before quietly saying, “Kelly-“
“What if Cruz didn’t get us out and you stayed, and I survived because you shielded me? What if you died protecting me and I had to fucking live with that, do you have any idea-“ His voice broke and he inhaled sharply, brokenly. He forced himself to turn away from Casey, running a hand through his hair and trying not to imagine waking up to a world where the man he had been in love with for so many years was nothing more than a corpse.
“You would have done the same for me.” Casey eventually said, and Severide turned around sharply to look at him.
“That’s not the fucking point.”
“I know it isn’t.” Casey tilted his head back against the firehouse with a sigh. The snow had caught in his eyelashes, the wind stirring his hair so that golden strands fell messily across his forehead. He was painfully beautiful, but Kelly had long since learned to breath through the longing that crowded his chest whenever he saw the other man.
"I would have done it for any of the men." Casey’s voice was quiet but resolute, his eyes boring into Kelly’s, "The fact that it was you just...” He laughed a little, helpless and strained, “You had to have known that I would never leave you there.”
(And Kelly certainly wasn't thinking about how it wasn't the order to leave the house that got him wanting to move in the end, but hearing Matt's voice shouting in the distance, urgent and ragged from smoke, drawing him forward like a moth to a flame because following Matt was muscle memory, following Matt was the only thing that made sense.
Or how he was the only thing that stood out in the hazy days since Benny died, the only thing that had stood out in the wake of Shay's death, the only thing that made him feel real when the world around him became murky and chaotic, how his smile- the one that seemed to be reserved for Kelly, the unguarded one that was a little shy and a lot wicked- made Kelly's heart lurch in his chest-)
“I’m not sorry,” Casey said when Severide didn’t reply, and Severide couldn’t have looked away from him if he had tried, “And I can’t promise you that I will act any differently in a similar situation, but I know how I would feel if you died saving me and I-“
Something inside of Severide snapped, and he strode forward and pressed Casey against the wall, crushing their lips together and swallowing Casey’s noise of surprise. Casey didn’t move for a few seconds, but before Severide could pull back and attempt to do damage control Casey slid his hands into his hair and pulled them impossibly closer, only drawing back briefly to breathe what sounded like finally.
When they forced themselves to part for air, Severide’s hands were framing Casey’s face and Casey had his fingers twisted in his sweater. Casey’s face was flushed, blue eyes bright and dancing, and Severide was going to dedicate the rest of his life to making Casey look at him like that.
He grazed his thumb across Casey's lower lip, voice low and a little raw, “Do you have any idea how long I’ve wanted to do that?”
Casey shot him a crooked, fond grin. “You could’ve done it ages ago, you idiot.”
Severide was about to reply and tell him that they had better make up for lost time then, chest so tight with disbelief and joy and love that he thought he may burst with it, when suddenly someone knocked on the door beside them. They automatically jolted apart, and the door opened to reveal a concerned-looking Boden.
“Is everything alright out here?” He asked, and Severide realized that the last time the members of the firehouse had seen them Kelly had been furiously dragging Casey outside.
“All good Chief.” Casey replied, voice impressively even and composed, and Kelly nodded in agreement, not trusting himself to speak without sounding utterly wrecked.
Boden raised his eyebrows, his face revealing nothing, but a few long moments later he nodded, “Alright then. Casey I need you to-“
Ambulance 61. Truck 81. Squad 3…
“That’s our cue,” Casey said, clapping Severide on the shoulder, and Casey and Severide slid past Boden and started to stride towards their trucks, only stopping once so Severide could bring his face an inch from Casey’s and whisper, “I’m still mad at you. For the record. But you could start making it up to me with breakfast after shift.”
Casey shot him a small but heart-stopping smile and kissed him once, briefly but hard. “Wear something nice,” he teased lightly, squeezing his hand once before jogging to his truck.
Severide ducked his head down, smiling ridiculously to himself and feeling something settle inside of him for the first time since Benny died, since Shay died, since the first time Matt looked at him at the academy with a fiery challenge in his eyes, before following.