Stiles is not Kate. Derek is older and wiser and says nothing of the arousal he smells on Stiles or how he spends most nights staring at Stiles in his room.
This is how it starts anyway.
Stiles waited a week after he turned seventeen to kiss Derek for the first time, blood splatters from a trickster fairy on his red hoodie still wet. He tastes of exhilaration, of adrenaline, of want. This kiss has been coming for a long time, and it's fast and rough and perfect.
Derek pushes him against a tree and devours his mouth, hands roving everywhere. Stiles is the one that pushes it farther and opens his jeans. He jerks Derek off, fast and a little mean, and Derek responds by pulling Stiles' jeans down and blowing him, uses all the tricks he knows to make Stiles scream. (He does.)
This is how it works.
Stiles talks too much and Derek doesn't talk enough and they fuck and it works. Stiles introduces him to his father and Derek receives the talk about how the Sheriff has friends in high places if anything untoward happens toward his son. (Stiles laughs and laughs and blows him in his room, daring Derek to stay quiet and Derek bite his hand and fists his hand in Stiles' hair and Stiles sucks him harder.)
Derek saves Stiles from vampires and Stiles saves Derek from harpies and along the way they hit the two month mark. Derek takes Stiles out to dinner and later fucks him the backseat of the Camaro because Stiles jerked off before they left and Derek could smell it on him all night.
Scott and Jackson and Lydia join his pack, Erica and Boyd come back, Peter hasn't tried to kill anyone, and Isaac is everyone's favorite. They manage to get along, and Stiles is the one to initiate movie nights and when Scott and Allison get back together he's the one that forms an alliance with Chris Argent and the Pack is at peace. Derek relaxes a bit and smiles more, and they're slowly becoming a family, bound by tears and blood and bites.
It's after they hit the six month mark that he realizes something is wrong. Stiles smells tired all the time and is worried about his senior year. They bicker more and it hurts. Derek knows what Stiles fears, and he knows how to get Stiles to stop arguing, tears in his eyes, and turn away. But Stiles knows Derek too, knows how one word can leave him gutted and whenever Derek hurts Stiles he hurts him back and they spend days not talking then fuck it out. Six months in and on the night of their anniversary Stiles is kidnapped and beaten and it takes three days to find him.
Stiles is even more quiet after that, and he doesn't want to go on anymore hunts. The Pack is confused because he's snappish with them too but he and Lydia spend hours talking about colleges and jobs and traveling and Derek leaves whenever they do because his chest feels tight. (He tries to say something once, but it comes out wrong. He tells Stiles that they can't go far, and one argument turns to another and he accuses Stiles of being selfish and that if he leaves how can he still be Pack? Stiles calls him a coward and that he's tired of hunting anyway. They don't talk for two weeks but when ghouls start robbing graves he's there with them to kill them. He goes to the house with Derek and they fuck hard and fast, but the next morning the do it soft and slow and Derek hopes that they're ok. He thinks that things will be better this time.)
Seven months in and there are good days when everything is golden and Derek sees his Pack around him and pulls Stiles in his arms and kisses him sweetly. (Stiles still laughs less but Derek treasures every one and at night he gives Stiles everything.)
Seven months in and there are bad days where even picking a movie leads to a yelling match and the Pack avoids them because it's ugly and Stiles will storm out with hurt and angry tears and Derek will stay and struggle to breathe through the feeling of Stiles taking his heart with him. (Sometimes Stiles comes back and sometimes Derek goes to him, but they still only apologize with their bodies and they try again.)
Seven months in and they've never said "I love you."
This is how it ends.
Stiles is eighteen and applying to collages. They're at the house, just them, and Derek knows what silence from Stiles means. Derek looks at him and keeps his hands hidden behind his back because his hands are itching to form claws and he can't show that he's nervous. (He's scared of what Stiles has to say because the last time he had this sinking feeling he was being pulled out of class and the counsellor had hesitated just like this to say anything.)
"We're not good together, Derek. We both had issues and we never worked past them and see where it got us. We can barely decide on a movie, for Christ's sake! Look at us! We fight all the time and we're miserable and I can't... I don't like who we've become, Derek. I don't like that when I look in the mirror I see a liar and a killer and I don't like how when I look at you I feel like blaming you."
"It's not because you're a werewolf, Derek, it's not. But I can't do this anymore. I thought I could, I thought I could be what you needed and still be myself but I can't. I can't and it kills me because we could have been great together but we fucked up and now it's messed up."
"I got into a college in Boston. I'm not coming back, Derek. I'm sorry."
Derek is frozen, feels faint and like the world stopped.
He says what he should have said six months ago, five months ago, yesterday, every night and every time. And it kills him to say it now because he should have said it before, should have noticed before and now Stiles is leaving and it's too late. (It's always too late, too late to realize the truth, too late to change the outcome, too late, too late.)
"Please. I love you."
Stiles' hands are shaking and he reaches out and cups Derek's face softly and Derek memorizes his face, broken and teary-eyed and lips trembling.
"I love you too. But we're not good for each other. And that's not fair to either of us."
Derek leans forward and presses their lips together, breathes in Stiles' scent, and takes a step back. He knows, has known for a while, that they were killing each other. But that doesn't mean that his heart doesn't feel like it will give out any moment when Stiles walks out on shaky legs and drives home.
That doesn't mean he's not lost and feels like he's fourteen all over again and told that his world just shattered.
(In two weeks Stiles will move to Boston and he won't come back. The rest of the Pack will stay with Derek, putting him back together and they won't blame Stiles but they won't say his name when Derek is there. In three years the daughter of a visiting alpha will smile at Derek and smell like jasmine and sweet grass and she'll ask him to dinner because Derek can't work up the nerve to do it. In six years the Sheriff will go to Boston to be with his son on his wedding day and will stay there for good. The Pack will receive invitations, but only Scott and Allison and Lydia and Jackson go. On the night of the wedding, Derek will tell her everything about Kate and fire and Stiles and loss and she'll understand and a year and six months after that it will be their turn to be engaged. Derek will send Stiles an invitation, and receive a blank card saying only I am so happy for you, Derek. You deserve this. In nine years he'll become Sheriff and go home to his wife and his children and when he hears the news that Stiles and his husband have adopted their second child, it will be the first time he doesn't feel any bitterness or regret. He'll hold his toddler and his baby and his wife and smile.
But that's later. )
Right now Derek is twenty-eight and Stiles is not Kate, but he's broken Derek anyway.
Right now Derek howls at the moon and cries for the first time in fourteen years.