I'm a huge sucker for Shikamaru/Naruto paired together. It's my favorite pairing for the Naruto series by far and even though I told myself I wouldn't upload things I write (I'm shy okay) I decided too anyways. There isn't enough of this pairing and it makes me sad. For my reasoning for how Sasuke can so easily switch focus it's because I just can't see him having any healthy romantic interest in someone. It will always be obsessive and shallow to me because Sasuke has always come off as someone with that type of personality. I've never liked him. Sorry if you disagree.
Naruto yawns and opens the door to the Nara residency. Scratching his belly as he gets ready to tell whoever it is to please come back later (he does have some tact, no matter what Shikamaru says) when he realizes it's not some random person but his teammate, Uchiha Sasuke.
"What the fuck, Teme. It's so early... why are you here?" He asks irritably and slightly curious. He can guess the reason though. Sasuke found out he was at the Nara residency and was going to try once again to have some sort of 'subtle' conversation with Naruto to make him realize that he 'loves' him like Sasuke 'loves' him. Which wouldn't happen since Naruto had never felt that way about Sasuke. For him it was purely brotherly. Like that annoying brother who you constantly bicker with and say you despise but know you'd have their back in a fight, because you're brothers.
He's about to say something else, to stop the upcoming conversation of Sasuke trying to express his 'feelings' when he notices; Sasuke isn't paying ANY attention to him. His attention is focused, like a hawk, past Naruto into the house. "Teme? Hey... Sasuke? What the hell are you looking a-" And he turns around to see what Sasuke is looking at only to see a very sleepy, not-quite-there Shikamaru drinking coffee in nothing but his boxers.
Shikamaru's standing there, yawning slightly and stretching (God those legs) as he blearily looks at Naruto. His hair is down, messy from sleep and flowing just slightly over his shoulders. The hickies Naruto ended up leaving all over his neck and shoulders contrast with his pale skin and dark hair nicely and Naruto briefly forgets Sasuke is behind him at the sight. Finally Shikamaru begins to make his way to the kitchen, apparently having decided whoever is at the door isn't worth the effort if Naruto is there.
Naruto (remembering that his teammate is behind him) is confused for a second as to way Sasuke is staring until it hits him "My boyfriend... my almost naked boyfriend is currently walking around half naked with evidence of what we did last night and my teammate is staring at him.".
Turning back to Sasuke, Naruto's about to ask "Why are you staring at my boyfriend? This isnt going to be a problem is it.". Thinking he'll see a murderous and jealous gleam in Sasuke's eyes but instead he see's something much different. Something that makes a snarl start to form in his throat. Sasuke is staring at Shikamaru much in the same way he stares at Naruto and nope, Naruto does not like that. No way in hell is he letting the Teme see anymore of his boyfriend, especially when the look in Sasuke's eyes easily says 'I want that. I will have that' with something darker lurking further behind.
Naruto narrows his eyes and growls, stepping in front of Sasuke's view of the retreating Shikamaru which causes the Uchiha to blink rapidly. He sees the anger and jealousy begin to rise in Sasuke's eyes but this time... Naruto's not sure if the jealousy is aimed at Shikamaru... or him.
Deciding to be as blunt as possible, as the dark spark he had seen in Sasuke's gaze is still there (Naruto knows it's not directed at him, that troubles him more than he likes), he growls low in his throat. "Shikamaru is my boyfriend. MY boyfriend (he's not sure why he needs to qualify that again but it makes him feel better). I don't care about whatever feelings you have for me but if you dare make a move on him or look at him like that again. I'll castrate you Teme. Believe it.". He watches the anger rise tenfold in Sasuke's eyes and his shoulders tense, looking for a fight. But Naruto is tired, he feels like his territory is being encroached on by his own teammate (who had just been making googly eyes at his almost naked boyfriend) and he wants to go snuggle said boyfriend and maybe go back to sleep very badly.
With that he slams the door in Sasuke's face leaving a very confused sexually and mentally frustrated Sasuke standing there. "When did Naruto get a boyfriend? How didn't I notice?!" Sasuke snarls suddenly before his mind snaps back to what he saw just past the blonde. "How did I not notice how hot the Nara was... and how do I catch his interest..." Is all Sasuke can think of as he walks off in a slight daze.