Remus wasn't sure how they'd ended up kissing.
No, that was a lie. He knew exactly how it happened. He was just still struggling to really believe it. When he'd entered Severus' rooms to ask about what time Harry was due back from the Burrow, he certainly hadn't expected things to turn out this way. Especially not when he'd entered and found Severus sat on the floor, back against the wall, knees up and head in his hands, cane on the floor beside him.
The other man looked up at Remus' shocked cry, watching him rush over and drop down in front of him.
"Are you alright? Did you fall, are you hurt?"
Severus didn't sneer at Remus' obvious concern, which would have been some comfort because it was what Severus did, but Remus fell quiet at the strange look in Severus' shadowed eyes. It was something like fear and anger and despair and regret all rolled up into one, and Remus found himself honestly surprised that Severus' voice came out perfectly steady when he spoke.
It was a clearly stated fact and that ball of emotions glinting in his eyes didn't come through in his speech. Instead he sounded... surprised, almost. As if he'd not truly realised it before, but now had and was only just coming to terms with the fact.
"My heart is failing and I am going to die."
"You might not," Remus said quietly. "You've still got chance to get a transplant."
Severus let his breath out in sigh. "Maybe."
Hesitantly, Remus laid a hand on the other man's knee. Severus glanced at it like he couldn't quite figure out what it was doing there.
"Severus, are you alright? Why are you on the floor?"
"Dizzy," Severus answered, still staring at Remus' hand. "Figured I'd sit down before I fell down."
"Wise idea. Are you still...?"
"Do you want some help to your room? Or chair?"
Severus blinked slowly and Remus felt very worried for him now, but the other man nodded jerkily. "Suppose I should."
He finally took his gaze from Remus' hand and grabbed his cane, accepting Remus' help to get to his feet, but once he was up he leant against the wall again, closing his eyes and leaning his head back. Remus kept a hold of him, just in case the dizziness overwhelmed him.
"You were wrong, you know."
He spoke so quietly that Remus doubted he'd have heard it if he wasn't standing so close.
"When? About what?"
Severus still hadn't opened his eyes, but the hand not holding his cane curled around Remus' bicep. Not to hold on for support, but just to hold on.
"You. Me. Last week. I never just settled for you. I wanted you both, you know, but I never... you were the only one I could have, but I didn't choose you just because I couldn't have her."
Remus became hyper-aware then of the fact that his arm was half around Severus' waist and there was really very little space between them. He could smell the bland aroma of the unscented soap that Severus used—it was really only unscented to humans, because everything had a smell and the wolf knew it—and far more strongly the simple scent of man, and a small mix various faint scents that could only be described as potions, even though Remus knew Severus hadn't been near a cauldron in over a fortnight.
All of a sudden, Remus felt like a teenager again, remembering stolen moments in broom cupboards and empty classrooms and behind trees at the edge of the Forbidden Forest, where they would exchange rushed, sloppy kisses, hoping no one found them because Severus didn't want his friends knowing he was not only queer but dating a Gryffindor, and Remus knew that if his friends found out he was dating 'Snivellus' then he'd never hear the end of it from James, and Sirius would probably do something incredibly stupid.
But he wasn't a teenager anymore, he had to remind himself. He was a grown man and so was Severus, who was a sick and dying grown man that Remus really should detach himself from before he did something ridiculous like kiss him—
And then Severus opened his eyes, dark eyes that were like tunnels into an abyss from a distance, but this close you could see the lighter rim around the outside that Remus had always thought was like the guiding light to lead you safely through the darkness, and he felt trapped in place, unwilling to move away because those eyes were beckoning him, he'd swear it.
Then Severus kissed him. Or maybe he kissed Severus. He wasn't really sure, but there were lips on his, tasting like pumpkin juice and something bitter that was probably the potions Severus took daily and that unnameable taste that was Severus. Remus let his eyes fall shut and felt a hand tangle in his hair, tilting his head slightly as Severus' mouth opened under his, inviting him to deepen it. He did, sliding his own hand further around the other man's waist to tug him closer and curling his other hand over the one of Severus' that held his cane, while his tongue slipped into Severus' warm, inviting mouth to brush against Severus' tongue. The blood was rushing in his ears and he couldn't help moaning slightly because god how he'd missed this, and it'd been so long since he'd kissed anyone and longer still since he'd kissed Severus, but he didn't ever want to stop.
Except he suddenly realised that the rushing noise he could hear wasn't just the blood in his ears—it was the floo.
That answers the question of when Harry's coming back, his mind provided unhelpfully as Remus, extremely reluctantly, broke the kiss and drew back, turning to look at the teenager standing just in front of the fireplace with a wide-eyed look of surprise on his face. Remus suddenly found himself unable to look at the boy; he'd always been awkward about displays of affection—even a friendly hug from the Marauders left him shuffling his feet and awkwardly clearing his throat—and getting caught by Harry in the middle of a kiss that made Remus feel almost like singing left him feeling extraordinarily embarrassed.
"Um..." Harry said, clearly feeling just as awkward about what he'd just walked in on.
Remus cleared his throat. "Hello, Harry. How was your visit to the Weasleys?"
"Erm... good. I'm going to the library," he said and darted towards the door, much to Remus' guilty relief.
Remus glanced at Severus, but his harsh gaze was fixed on Harry.
"Not a word to anyone," he growled. Harry gave a quick nod and vanished through the door, leaving the room in a heavy silence.
Remus looked at Severus. He still had his gaze on the door and the open emotion that'd filled his eyes earlier had vanished to leave his black stare cold and hard. Remus knew what was coming. That was the same expression Severus had got after the frantic, hurtful exchange they had in sixth year after Remus and Sirius walked in on Severus with Regulus Black. While Sirius had confronted his brother in a shouting match that ended with a fistfight that landed them both in the hospital wing, Remus had confronted Severus in quiet hurt tinged with guilt and shame. They'd both ended up with bruises as well, but their bruises were finger-shaped on hips and mouth-shaped on necks, and Remus had savoured them for the short time they'd lasted because they hurt less than Severus telling him in a cool voice that he was never going to touch an animal like Remus again.
He didn't say that this time, just straightened up, turned without looking at Remus, and said simply, "I'm going to bed."
Remus could have stopped him of course. Given Severus' weakened state, it'd have been all too easy for Remus to pin him to the wall and demand that Severus not brush him off, that he accept what'd just happened, that he admit to maybe wanting Remus like Remus wanted him.
But he didn't. He told himself it was because Severus should go to bed and rest, but mostly it was because he was scared Severus would look at him and say that the kiss was a mistake, that it meant nothing, that Severus never wanted Remus like Remus wanted him, and that, worst of all, it would be the truth.