Billy starts to take note after a fourth shirt goes missing. He finds them two days later, accumulating in a pile on Steve's bed. Billy doesn't really mind, he's always had a soft spot for the brunet wearing his clothes. Finds it hard to deny his pretty boy anything when he peers up at him with Billy's leather jacket wrapped around his shoulders like a possessive lover, his scent lingering on Steve's skin. He does grow concerned though, when half his wardrobe winds up in Steve's room, and there's hardly any space left for them on the bed.
Billy comes to the realization that Steve is nesting not too long after that.
He freaks out internally due to the very specific implications that go hand in hand with nesting behaviour, and fuck, Billy can barely handle Max and the nerds who won't leave Steve alone, he's not ready or qualified to be raising a kid of his own. But deep down, Billy knows he will do anything to support Steve. He will never be like his piece of shit father when it comes to this. Still, he can't help but feel a little hurt that Steve hasn't said anything about it to him.
"Maybe he doesn't want you to know. Maybe you're just not good enough for him," sneers the vicious voice in his head. Billy pushes those thoughts away before they get the chance to manifest into something darker. He's worked too hard—Steve has worked too hard—for him to drown himself in that type of negativity again.
Steve finally gets fed up with Billy after a week of him glaring at anyone who comes too close. His mate has been spending a concerning amount of time staring at his stomach, as if an alien's about to pop out and bite his head off, and that's starting to freak Steve out. He corners Billy with crossed arms and all but forces the other boy to fess up about what's been making him act so strange. Steve goes slack-jawed and feels his cheeks heating up when Billy mumbles the words "nesting" and "baby", while keeping his gaze fixed to the floor.
Before Steve can say anything to correct him, Billy's hand shoots up to grab his wrist, and with a tremulous voice which grows firmer with each passing second, the blond tells Steve that no matter what happens, he will never abandon him. That he'll be better, that he'll prove himself worthy of providing for Steve.
"Just give me a chance," Billy begs with his eyes, full of anxiety and fear and resolve.
Steve absently notes the slight tremble of the fingers rubbing gentle circles into his wrist, and feels as if his heart is about to burst. If someone told him a year and a half ago that the asshole who almost smashed his face in would be making him such a promise, he probably would have laughed that person out of Hawkins. So Steve takes a second to swallow the lump in his throat, and leans forward to rest his forehead against Billy's.
It takes him twenty minutes to convince the blond that he's not pregnant, and no, he's not just saying that because he doesn't want Billy involved. The other boy relaxes and slumps against Steve when he finds only sincerity in the brunet's voice. Pressing a kiss to to the mating mark on Steve's nape, Billy smiles with a possessive curl in his stomach when he feels his pretty boy tremble. Billy asks Steve why he's been nesting after a moment of silence, and Steve shrugs helplessly because honestly, he doesn't know either.
Now curious, Billy discretely borrows all the books he can find on the subject from the local library, and works his way through them whenever he gets the chance. He discovers that while nesting behaviour is exhibited most commonly during pregnancy, it can also occur when a mated Omega feels safe and protected, especially if the Omega has suffered from insecurity and anxiety in the past. Billy reflects on Steve's body language when they first met, thinks about the way his mate would fidget with anything he can get his hands on, thinks about how he'd wrap an arm around himself even when he's wearing the mask of King Steve.
When the implications of Steve's current behaviour sinks in, Billy feels warmed to his core, almost dizzy with the revelation. Even after all this time of being with the brunet and making amends for his past mistakes, there is still a part of Billy that feels like he doesn't deserve him, that he's incapable of redemption. Steve, who is sweet and kind and forgiving. Steve, who somehow fell in love with him when he was at his worst and helped him change for the better. Billy knows about the brunet's abandonment issues, which started with his absent parents and got worse after his breakup with Nancy. He's been jerked awake more than a few times at night by Steve's terrified cries, his pretty boy haunted by monsters even in his dreams. The thought that Steve feels safe and secure enough with him to nest makes Billy want to sob in joy and relief. For the first time in his life, Billy feels like maybe he's worthy of love after all.
The next day, Billy goes to the store and buys the softest sweaters he can find. He will never be caught dead wearing these things outside—he's still got an image to maintain and they look terrible on him—but at home he slips them on and scents them. The books all said that warm and soft materials are the best for nesting, and while Billy loves his denim and leather, they're really not that comfortable for Steve. By this point, it's an open secret among their friends that Billy will do anything to make his mate happy. (Nancy likes to joke that Steve has Billy wrapped around his fingers, and Steve just smiles knowingly at her teasing. He's glad that they were able to remain friends after everything that's happened between them, even if it did hurt to look at Nancy for a few months after their breakup.)
Steve is delighted when he finds the soft sweaters in Billy's closet, and makes a habit of wearing his favourites around the house. The rest gets added to his ever growing pile, which has pretty much taken over his bed. Billy will claim no knowledge of how they got in there, but Steve knows his Alpha well enough by now to see through his act. Billy has always been better with actions than words, and Steve has long since promised himself that he will never take how much his mate cares for granted. (The way Billy's eyes darken with desire when he sees Steve walking around in nothing but his sweater on is an added bonus.)
There are still nights when Steve wakes up with his heart racing, gasping, and sweating from the creatures that claw at him from the corners of his mind. But buried under a cocoon of warmth and surrounded by his Alpha's scent, Steve no longer fears what may be lurking in the dark. When Billy pulls him close and calms him with soft kisses and whispers of sweet nothings onto his skin, Steve lets himself be lulled back to sleep in his mate's gentle arms. Knowing, with a deep-seated sense of belonging, that he will still be there when the morning comes.
Author's notes: Apparently I've fallen into the pit that is Harringrove and now I can't stop thinking about these boys. This headcanon wouldn't leave me alone, so I hope you guys got some enjoyment out of it! This is also the first fanfiction I've written in 10+ years. I'm so glad that I finally sat down and completed a story, even though it's not very long. Many thanks to the Harringrove fandom for all the inspiration you've given me, and I'm so glad to have finally broken out of my long, long hiatus from writing.