Theo and Brody share a very interesting and funny dynamic what makes this relationship active and special. Their both very sassy and when it comes together it can collide sometimes. However, Theo and Brody didn't share something special at the beginning of their adventure. Indeed, they were dating each other best friends; Theo was dating Patrick Dunbar and Brody was dating Jackson Whittemore. They were always together, mostly because they were hanging out with their boyfriends and best friends but didn't really had anything in common. What makes their relationship funny is when Theo still acts being a jerk sometimes to other students, which are mostly Gryffindors. And Brody on the other hand can be pretty sassy too, but he still acts like everyone's friend who cares and behave.
Brody met Theo officially in 1993 on the same day as he have met his love of his life; Jackson Whittemore. Brody thought Theo was a nice Slytherin guy, but was always intrested in his best friend, Jackson. Brody supports Theo in every Quidditch match he plays, and because he is the Quidditch commentator, he dish Theo up by making him a fantastic player (by words).
Brody and Theo become closer when Brody found out he and his best friend and stepbrother Patrick were dating in secret. Because Patrick is Brody's best friend and brother, he wants Theo to promise him that he would protect him in every way he could, which Theo accepted. Brody supports their relationship and together with Jackson, the four are having much dubbledates at Hogsmeade.
Brody and Theo's friendship started to development in 1995 when Patrick broke up with Theo and Jackson broke up with Brody. Brody and Theo kinda grew closer in a way what made both of their exes very nervously sometimes. However, they both agreed that their friendship stood away from the others relationship problems and hung out more in their free time. By that, Theo and Brody hung a lot in Derek's pub were they could talk about things they never thought they would know of.
At the start of the First Wizarding War, Brody development his feelings about Theo; not in a romantically way. He wouldn't be suprised that Theo would stand for Tom Riddle's behaviour what takes his trust in him away. It kind of ruined their special friendship, but on the other hand, Brody's doubts came true when Theo joined the Death Eaters and fought with Voldemorts warriors. Upset and dissapointed were exactly the things Brody felt about that. How could he do that to his friends, and especially Patrick since he was also a part of the Elementals.
Somewhere at the big battle of Hogwarts, Theo's body was found under stones and blocks with Brody in presence. Theo was dead and however Theo stood for, Brody did feel sad about the death of his former good friend.
After the war, Brody got selected to be the new Head Auror and found out by visiting Azkaban that Theo was still alive. Theo explains he was a spy for Albus Dumbledore and got unmask by Voldemort in the battle and faked his death so everyone believed he died so he could rot in Azkaban. Brody, who first didn't believe he could do that to everyone, reacts with anger what made Theo angry too. At the moment Brody wanted to leave Theo in there, Theo pushed him against the stocky wall and from anger and agression, it turns into a intime moment. They both were hurt, lonely for a long time and when they looked deeply in each others eyes, a moment of a romantic kiss came between them which ended in a hook up in Theo's cell.
After Theo was acquitted in 2004, Brody helped him back on top by offering a job as Auror second hand, together with follow slytherin Santana Lopez. Brody and Theo started to trust each other again and started to grew closer. However, in Patrick's precense, the two still act awkward to each other which made Patrick curious what happend between the two. Theo doesn't want Patrick to know about what happend in Azkaban. However, Brody disagreed and told his stepbrother what happend and that it didn't mean anything for him.
With Patrick knowing between their One Night Stand, the two still got to see each other for a while, what turns to be more than just friendly talks. Theo and Brody have a lot of sex in secret. Although they didn't feel romantic feelings for each other, they just find the attention and the voltage entertaining. This sexual relationship ends when they both wanted to start their lives back on top with their soulmates, and after that the sexual activity stopped.