A/N: Obligatory copyright statement - I do not own Teen Wolf, nor any of the characters represented in this story. It is purely a fan fiction plot bunny that has been rattling around in my head and is inspired by 2 different stories: The Thin Wall by Tassos and Tumbling Down by dornfelder both on Archive of Our Own.

It happened almost three months after the Alpha Pack left. Three months after Derek and Stiles finally admitted their feelings for each other and Derek realized that Stiles was his mate, but had yet to tell Stiles or fully claim him. Erica's first heat came after the Alpha Pack returned her and Boyd. The Alpha Pack were there to teach Derek how to be a proper Alpha. All of the wolves were now united under his leadership and the pack was finally coming together. Even Stiles, Lydia and Allison as humans, had a places in the pack. Stiles just didn't understand his yet.

Erica's first heat was something of a shock to everyone. Realistically Derek should have known that this would happen as an unmated Alpha and even though he knew Stiles was his mate, he still hadn't claimed him. The instinct to reproduce was strong in an Alpha wolf. Derek's human side knew that Boyd and Erica were mates, and he knew that he didn't want to hurt Stiles by forcing him into a life-long commitment as his mate.

As her cries became unbearable, Derek finally admitted to Stiles that she would continue to be in incredible pain until the Alpha knotted her to ease the heat. Boyd wasn't and wouldn't be enough even though he would stay by her side throughout the three day heat. Stiles was at first shocked and incredibly hurt by Derek's timing to divulge this information. Stiles had done his research on heat cycles and mating and knew exactly what knotting a beta female would mean in the long-run. Condoms were not an option for werewolf knots. Dr. Deaton created a powerful contraceptive that would stave off imminent pregnancy, but Stiles knew it was only a matter of time before nature intervened and Erica ended up pregnant from Derek. Reluctantly, Stiles told Derek to go help her as he was feeling nauseous for letting his friend and pack mate suffer when there was a solution, even though a flicker of jealousy burned its way through Stiles system when Stiles realized that Derek had never knotted him.

Stiles is fragile, human, easily breakable. Derek had never offered to knot him and even told Stiles that he wouldn't for fear that it was hurt Stiles when Stiles asked. Derek was gentle, thoughtful, and careful when fucking Stiles and Stiles started to resent him for it. He wanted everything Derek could give him. He wanted the Alpha and the man to fuck him without abandon, snarl and grab him so hard there would bruises on his hips, but most of all knot him and tie them together. But in reality he was resenting his own humanity and saw himself as a liability for everyone in the pack. He wanted the Bite, but when he asked Derek refused saying, "Stiles, I won't give you the Bite just because you want me to knot you."

Three months after Erica's first heat, she had her second. Her third followed three months after that. Each time Stiles heard the sounds of Derek snarling and pounding away and Erica's moans of pleasure he let the hurt and jealousy seep even further into his heart. It was poison in his veins. He stopped his constant rambling. His rapport with the rest of the pack was strained and he felt himself pulling away from group events that involved Erica. He knew it wasn't her fault, but he couldn't help his feelings of inadequacy and constant jealousy so he decided distancing himself from her was the best option.

Derek knew what he was doing to Stiles and their relationship, as well as the whole pack dynamic. He could feel the glares from Scott, Isaac, and Jackson each morning after. He saw the looks of disapproval from Lydia, Allison, and Peter. He hoped that the damage wouldn't be irreparable, until Stiles issued an ultimatum as he solemnly left their bedroom to end Erica's suffering again, "If you get her pregnant Derek, I will leave you." Those words left a gross feeling in the pit of stomach and a hollow feeling in his heart. He knew Stiles was serious. He could see the way that Stiles eyes had dimmed over the course of the past nine months. His normally bright and sunny exuberance was replaced by someone who was quickly becoming dulled and sullen.

He mentally berated himself for letting things get this far without confessing that Stiles was his mate, but what could he do now? If he told him, Stiles still might decide to leave him for not claiming him back when this all started. If he didn't tell him, Stiles would inevitably leave him when Erica was finally bred and pregnant. So Derek did nothing for the time being, praying that Erica's heat wouldn't result in pregnancy.

Three months later, Erica went into heat and Stiles stayed away from the house. He knew that there had to be options that were being overlooked. He didn't want to leave Derek, he truly loved him, but it was looking more and more like the eventual would happen and Erica would get pregnant and Stiles knew he couldn't be with Derek anymore.

Stiles decided to contact one of the Alpha's that had come to town. Ethan was main reason Derek finally admitted his feelings for Stiles after Ethan tried to date him while they were training Derek.

"Ethan, it's Stiles." Stiles stated over the phone while driving to a hunting cabin that his father used every year.

"Stiles! How are you? What can I do for you?" Ethan responded.

"Well, I have a little problem and I need your advice. Would you be willing to meet me somewhere so we can talk?" Stiles asked, hope filling his voice. Ethan was an Alpha from a pack in Southern Oregon and only 2 hours from his Dad's hunting cabin outside of Beacon Hills.

"Of course, Stiles. Is everything okay?" Ethan sounded concerned which made Stiles breathe a sigh of relief. "Well, I'd rather talk about it in person if it's all the same to you. I'll text you the address of my father's hunting cabin. It's outside of Derek's territory, so please do not let him know that we are meeting." Stiles pleaded. "Sure. See you in a few hours." Ethan said.

Stiles got to the cabin and set about making sure it was livable for a few days. He sent a text to Derek saying he was okay and staying away while Erica was in heat. He didn't tell Derek where he was, nor did he expect Derek to look at his messages since he was undoubtedly going to be distracted for the next three days. What he didn't know was that as soon as he left the territory, Derek felt an unbearable shot of pain in his heart that immediately made his knot deflate and slip free from Erica. He writhed on the ground for a few minutes and even though his Betas had rushed to his side at his screams of pain, all they managed to gather from him before he passed out was, "Stiles."