For as long as he had known him, Steve had been a pain in Bucky's ass. He was a ninety pound tornado on a good day, standing up to betas and alphas twice his size and not letting his sickly omega body hold him back at all. Bucky loved his fiery spirit, but god, he was going to get himself killed one day.

And Bucky was going to be goddamn sure he wasn't going to be the one to kill him.

It sounded so easy. Bucky loved the little spitfire. Why would he ever do anything to hurt him? But Steve was a thin layer of skin and bones held together by sheer stubbornness. Bucky was terrified he was going to break him in half every time he took him in his arms.

And Steve wanted sex.

It was the worst idea in the world. Steve had asthma and heart trouble and shouldn't be exerting himself. But Bucky didn't really know how to say no to his Stevie. And he would have felt bad if the love of his life died a virgin. Steve took great delight in behaving wildly inappropriately for an omega, but he still had to have some instincts. And they had to be clamoring for him to get fucked and mated like a proper omega.

Well, Bucky would fuck him at least. Mating was out of the question. Steve's body was too fragile for a knot. But he knew better than to tell Steve that. It would only make him more determined to prove him wrong.

So all Bucky had to do was fuck his omega and just not knot him.

How hard could that be?

—

Steve groaned and fisted his hands in Bucky's shirt.

He hadn't understood at first why Bucky hadn't taken it off with the rest of his clothes. But now he was grateful. It gave him something to hold onto, something to ground him as Bucky's fingers slowly stretched him open.

"You know, we don't have to go all the way tonight," Bucky murmured. "We could just stick with fingering this time." As if to prove his point, he curled a finger just right.

Steve gasped in pleasure and his hands tightened in Bucky's shirt. "Oh god. That feels real good, Buck." With an effort, he refocused on Bucky's suggestion. "I appreciate the offer. But it's not all about me."

Something like disappointment flickered across Bucky's face before his expression settled into fond amusement. "You're too selfless for your own good, Stevie. You can't lay back and let me take care of you for one night?"

"Nope," Steve said cheerfully. "If you finger me, then I'm going to have to make it up to you with a blowjob and-"

"Not with your asthma," Bucky said firmly.

"Exactly."

Bucky rolled his eyes. "Alright. If you're sure about this."

Steve tried not to whimper as Bucky pulled his fingers out, reminding himself that the empty feeling was only temporary. He was soon going to filled with something so much better than fingers.

Soon might have been a little optimistic. Bucky was taking his sweet time pressing into Steve's body, moving forward what felt like a millimeter at a time. Just as Steve was about to take matters into his own hands and force their bodies together, Bucky finally bottomed out.

Oh.

Oh, that felt good.

So good.

Jesus Christ, why hadn't they done this sooner?

"Hey." Bucky waved a hand in front of his face. "Still with me, Stevie?"

Steve blinked. "Yeah, I'm with you."

"Good." Bucky's smile was a little shaky. "Can I…can I move yet?"

"Go for it."

Steve didn't think anything could compare to the wonderful feeling of fullness, of Bucky's body wrapped around him and inside him at the same time, but he was willing to keep an open mind.

Bucky sucked in a breath, braced his hands on the mattress, and slowly rocked his hips forward.

Okay, Steve stood corrected. This was so much better. And it got even better as Bucky sped up, each thrust becoming more and more confident.

Steve found himself helplessly bucking his own hips up to meet each of Bucky's thrusts.

"Oh fuck," Bucky whimpered. "Oh fuck. Stevie, stop moving. I'm going to pop a knot."

"That's the idea," Steve panted. He twisted his fistful of Bucky's shirt. "Give it to me, alpha."

"Oh hell," Bucky gasped. "Stevie. Stevie, please. I just wanna get you off."

"You are. I can feel it. So close."

Bucky whined low in his throat. His hips stuttered to a halt and his eyes rolled back into his head.

Steve's insides were filled with warmth and then the slow-building pressure of Bucky's knot inflating. It was an intense feeling almost bordering on painful, but after a moment, Steve's body adjusted. And then it was nothing but pleasure. Sweet, sweet pleasure. His body was stretched to the limit, but he felt gloriously powerful, able to handle anything and everything. He'd never felt more alive.

But then Bucky suddenly came back to himself, eyes wide with panic. "Oh shit. Oh shit. Stevie, are you okay?"

"I'm fine," Steve said. Even partially passed out from great sex, Bucky had done an admirable job not collapsing on top of him.

"Oh hell. We shouldn't be doing this." Bucky jerked backwards and then winced. "Fuck, that hurts."

"Of course it does, genius. Didn't you pay attention to knotting in biology? Neither of us should be moving until the knot goes down."

"My ma's going to kill me," Bucky whined. "And then your ma's gonna kill me. I'm a dead man, Stevie."

"My ma's not going to kill you," Steve said soothingly. "She likes you."

"She's not going to like to like me if I knock you up." Bucky groaned and rubbed a hand over his face. "Fuck. I should have listened to my ma. 'Don't you knot that boy,' she told me. 'He looks like a stiff breeze could knock him over. He's not going to survive a knotting.' And I've knotted you anyway. Fuck."

Steve rolled his eyes. "Don't be ridiculous, Buck. Your knot's not that big."

"Fuck you, Steve," Bucky growled. "My knot's plenty big."

Steve rolled his eyes and canted his hips upward.

Bucky whimpered. "Stop it, Stevie. I'm going to come again."

"I thought that was the point," Steve said. "Get your knot to go down and get it out of me as soon as possible so you can fuss over me like the mother hen you are and make sure your giant alpha dick hasn't ripped my insides apart."

Bucky's face paled. "Wait, is that what it feels like?" He cupped his hands around Steve's face. "Stevie, baby, did I hurt you?"

"No, you idiot. That was sarcasm."

Bucky huffed. "You can't say things like that. You know how much I worry about you."

"You don't need to. I can take care of myself."

"Not what my ma and your ma said.

Steve huffed. "I don't care what they say. I can look after myself, I can look after you, I can look after any potential future pups we may or may not be having. He frowned. "Do you actually want pups?"

"Hell no. I have a hard enough time keeping you from running headfirst into danger. I don't want to be chasing after pups too."

Steve snorted. "Then that's settled then. We won't have pups and our mothers won't have to kill you. Now can you stop freaking out? I want to enjoy my first time getting knotted."

"First time?" Bucky said in a high, panicked voice.

"First of many," Steve said cheerfully. "Listening to all your whining hasn't been fun, but getting all your stress out in the open is good. We really need to do this more often. Stick both of us together for twenty minutes, all we can do is talk. I'm thinking we need to do this at least once a week."

Bucky heaved a sigh. "Don't know what I was thinking, letting you start having sex. Shoulda known better."

"Yeah, you should have." Steve snuggled into Bucky's arms. "But we're not stopping now. I'm too used to it already."