So, a short warning: I've reconstructed the whole family tree of every family in this story. Some people have different parents, some people have one canon parent and a whole different character as their in-story parent...
Here is the full tree on Sansa's side ( 66. media. tumblr 101f95e0b24ebdb35511bbcc884b1c02/f278cb5f3f7ba6d0-e1/s1280x1920/da23186dc5794f203768c2476286959884710dc2 .jpg ), just remove the spaces.

I will update it as the story goes (who dies, who is born, who marries who, who divorces who...), but the story explains everything very well - don't trust me? Trust my beta reader who understood the basics without me explaining everything.
That is all. Enjoy the chapter.

Sansa took a long and deep breath, staring at herself in the mirror. The wedding dress looked perfect on her, but her eyes could barely register it.

"You don't need to do it," Eddard touched her back. "We can find another way."

She just kept staring at herself in the mirror. Her face was cold, and her eyes were digging so deep into her own reflection that Sansa could feel her soul breaking into pieces.

"They are waiting for us," she reminded him. "Everyone."

The princess closed her eyes and then opened them once again.

"They need us," she reminded him. "Come on. Let's go."

Ned held her arm, walking out of his daughter's chambers and through the corridor while the staff watched them.

Eddard and Sansa were alone. She was an only child, having lost her mother early in life along with an unborn brother, and was the obvious future queen. It's not like they were in a full monarchy, though, but their roles were important. Her father's decisions were always to be accompanied and measured by the parliament and his authority had limits these days, as well as hers would. Still, there were things she needed to answer for and alliances that still required her. That's why she was in that dress today.

Jon Rhaegar Rodwell Nymerios Targaryen was the prince of a country close to theirs, much smaller but that needed their help. They were currently in a war, running out of soldiers and even food, and his older brother – King Aegon, the first – had approached her father with a proposition of exchanging his younger brother for full support. Eddard wanted to refuse, stating Sansa wasn't a coin to be exchanged, but she didn't. She was getting older – the two of them were – and the pressure to find a husband was turning her life into a mess. Every man she could ever meet was trying to get a place by her side or, worse, her bed. Everyone who approached Sansa wanted something and she couldn't take that any more.

The princess waved outside with a large smile while people cheered around them.

"We can still leave," he affirmed when the carriage stopped in front of the church. "We can leave, just say the word."

Sansa shook her head, squeezing his hand.

"Come on, dad," she smiled once again. "I'm not going back now."

The king walked her into the huge cathedral and the two stopped to talk to the bishop. She couldn't hear them, as Jeyne – her maid of honour - fixed the back of her dress and positioned herself along with the bridesmaids and the page boys.

When Sansa and Eddard finally started walking, she had to tell herself out of squeezing her father's hand too tightly or walking too slow – or fast. Her smile was almost painful to hold. She could feel the hand around hers tightening when they lied eyes on the man standing with his back turned to them beside his brother – the king. Jon was strong, with large shoulders and strong arms that could probably lift her up with no effort, but shorter than her.

When he turned and looked at his bride, his eyes were the most grey Sansa had ever seen in her life, even greyer than her father's, beautiful and bright. She couldn't hear the words spoken to her, not with him looking at her with the corner of those eyes. When he turned to face her, he couldn't raise them to her face, but his voice was firm and his grip tight on her hand as he said his words.

"I, Jon Rhaegar Rodwell Nymerios, take thee, Sansa Alys Raya Gilliane Lynarra, to be my wedded wife, to have and to hold from this day forward, for better, for worse; for richer, for poorer; in sickness and in health; to love and to cherish, till death us do part, according to God's holy law; and thereto I give thee my troth."

Sansa took a long breath before it was her turn. She and her father had had a long discussion about what she was going to say and how much that would mean.

Don't make promises you can't keep.

"I, Sansa Alys Raya Gilliane Lynarra, take thee, Jon Rhaegar Rodwell Nymerios, to be my wedded husband, to have and to hold from this day forward, for better, for worse; for richer, for poorer; in sickness and in health; to love and to cherish, till death us do part, according to God's holy law; and thereto I give thee my troth."

She could see the moment on Jon's face. The single, small word she'd left out that made his jaw twitch and his eyes to freeze on her face. Sansa could feel everyone staring at them, from King Aegon to her husband and every single person inside the building.

Obey.

She didn't promise to obey.