This is kind of AU-ish, nothing in season three happened except that Rufus and Lily got married. Serena is at Brown, Dan and Blair are at NYU and Chuck and Blair are still together
Dan
As the sun began to peek its way over the horizon like it did yesterday and the endless stream of days before that, Dan sat in amazement wondering how he'd spent most of his life missing out on something so breathtakingly beautiful. Though he had experienced something, someone of equivalent beauty perhaps more so than the sight nature had put on display for him and him only as his ran his hands through the soft white sand. She and the rest of his recently enlarged family were probably still sleeping soundly in silk sheets and air conditioning. Even if the large mansion boasted acres of greenery, swimming pools and halls and halls of decadence screaming 'money!' it was crowded and unpleasant and he wondered how exactly he was supposed to be spending the next two months 'relaxing' in the Hamptons with a girl he so wasn't over and acting like the best of siblings. No. One day was enough. He could deal with the occasional run in back in the City and the friendly conversation over waffles but this? No. He never really looked at her, deciding it would only cause problems for them both. After all, they'd grown apart. It saddened him now as he sat here with his thoughts left to ponder the reasons why they had in the first place. They were young. They still are. The last thing he wanted was for them to turn into their parents. Unresolved and left unsaid only to reunite when their lives are half over and fuck around with everyone else's.
Rays of golden light reflected their way across the water, dancing in front of his eyes. He tried to prepare himself for falling right back in love with her again. He'd even walk around with his shoes untied to speed up the process simply because he missed the feeling. Though the more he thought about it, the more he realised he wouldn't even need to. He had never fallen out of love with Serena Cecilia Van der Woodsen. He'd merely taught himself to live without it. Finding substitutes during his freshman year at NYU and hoping to gain some fulfilment from the stream of women that he would've – in some parallel universe – found attractive.
As if the smell of summer had cleared his head, he realised what and who he wanted more than anything. The same thing he'd always wanted since his start at St Jude's all those years ago. Summer was her season. The July baby had some other worldly connection with the season and Dan watched in awe as all the features that he loved spun out on some natural high and began to intoxicate him without permission or warning. She made him feel sixteen again; she made him feel as being sixteen was thing best thing in the world. Her flirtatious yet immature laugh resounding through the house, the flick of her long blonde hair, the body better than any supermodel, the gorgeous heart that could melt his own and the flash of those striking blue eyes haunting him with the fact that all of it was once his and he lost it all.
The way he was going, he was on the fast track to premature insanity what with both his dreams and his waking moments tormented by the memory of a girl, the girl who stole his heart and made it her own.
Dan made his way back to the house dreading the return the enclosing feeling he'd just managed to shake. He had no idea what time it was but as soon as he walked through the door he was hit with the smell of fresh waffles and maple syrup. The cool air washed over his skin calming him down momentarily and he made his way to the overt kitchen.
"Dan, nice of you to join us," he noticed the sneaking sarcastic tone to his father's voice but he had no interest in retaliating as his eyes passed over the large circular table and the mountain of food that had occupied the majority of it. Serena, Jenny and Eric were already wet, probably from the pool and Lily perfectly dressed.
Dan mumbled a good morning before moving to sit next to Jenny. Although it was after he sat that he noticed that Serena had moved over to make room next to her. He cursed himself as caught the brief hurt expression he'd become too accustomed to as it crossed her face for a flash of a second. It's for the best, he thought to himself.
Serena
Serena sat cross legged in front of the French windows in her room, content, as the tangerine light warmed her skin. She'd been doing the same thing every summer morning since she was eight. Her room at the Hamptons house hadn't changed much at all. There was still the same queen sized bed, the Greek Islands – inspired decor and the wide sun lounge.
Although her mind was now less dazed by the sunrise and more preoccupied by the fact that Dan was staying three doors down from her. Her heart fluttered at the thought, she closed her eyes and tried to steady her breathe. They were step siblings now she reminded herself, but siblings nonetheless and there was nothing she could do about that. It was as if the universe had played some massive joke on them, well, at least her. She'd seen the Gossip Girl blasts about Dan, even in Providence. "Lonely Boy to Playboy" and the like, while she had practically spent the entire year alone, moping around Brown whilst continually telling Blair that she was fine hoping that the more she'd said it the more likely it'd come true.
The parties bored her now; same people, same music and the alcohol tasted bland, no longer providing the escape she was looking for. Serena was now almost at the top of all her classes; she did her assignments, attended her lectures and more or less fell into the traits that her best friend prided herself on (minus the schemes and games) surprising both Blair herself and her mom.
Like always, there had been one exception of course.
One rainy night in Late February her roommate Jess brought two of her friends, Russian vodka and a whole collection of sappy romance movies. The whole ordeal left her in a drunken mess. The three other girls had fallen asleep on the floor but Serena held her phone up to her ear as she slouched against the wall. It was probably some ungodly in Manhattan but Blair picked up on the third ring.
"S, what is it? I have an exam tomorrow," she finished with a yawn.
"I'm so sorry B, you were right. I don't know what I'm doing," her voice quivered, her eyes full and watery.
"Right about what? S, are you drunk?" Blair had far too much experience with Serena's escapades but it didn't stop the worry from coursing through her veins. It was the same story over and over. Serena would build these protective walls around herself only to have them crumble around her.
"About Dan B, about everything; it hurts. I just want to stop, I- I want it to go away," her tears began to fall now soaking her shirt.
"I know sweetie, I know it does. How about you get some sleep and we'll talk about it tomorrow. I love you,"
"I love you too, B."
Serena knew that Blair had been waiting for that confession for months but she didn't show the satisfaction of being right. In the morning she let Blair convince her that she and Dan would get the time to sort out their problems but in the mean time she would have to be patient.
Finally her chance had come and she would make the most of it.