Theodosia and Philip

They meet.

Philip and Theodosia were really good friends. They originally just started talking one day when they were little when Alexander and Burr were together doing something (arguing I expect) and found out how much they had in common. So they kept talking.
Once their fathers found out they were friends they got so mad that the two hung out even more just to piss them off. They would walk through town for hours just rambling away about their father's plans and how similar they are even though they will never admit it.
When Theodosia got her first crush (could be any gender because no sexuality was mentioned but I'm going to go male cause it was so much harder to be lgbt+ then. Even if I do believe in Lams.) Philip made sure to meet up with him and make sure he would be a good guy for his Theo. She was like a sister to him. More so even than his biological sisters. He had to make sure she would get the best.
When Philip went away to King's College -renamed sometime in the time he went there to Columbus University- Theodosia became depressed. She didn't have her brother living just down the road anymore. He was off at school. They still wrote to each other but it just wasn't the same for her. Philip would tell her all these stories of the people he was meeting and what he was learning and he promised at the end of every letter that he would pass the knowledge onto her.
The day Philip graduated and challenged George Eacker to the duel he went to see Theo before he even went to his family. He told her what George had said and broke down crying in front of her. She had never seen her friend cry like this before. He cried when they were little as kids do, but he hadn't cried for years. Not even the day the Reynolds Pamphlet came out. She could tell how terrified he was but she had no idea how to help him. So she told him to go home and ask his father how to handle it. She knew he had fought in the war and she knew he was his best friend's second in the duel against Lee.
After Alexander gave Philip his spiel about aiming at the sky Philip went back to Theodosia's. He told her what his father said. Then he asked her to be his second. He knew that she was a girl and that it was technically against the rules but it never actually SAID no women. But this was his best friend. His only friend after his father's affair. She was the one he wanted by his side if he was to die that day.
She said yes.