Opinion: There’s no way Draal and Nomura’s past relationship was safe from troll politics. A changeling and the Trollhunter’s son? That can’t have been coincidental. One of them was using the other, and even if feelings developed they developed in the midst of a high pressure microcosm of troll/changeling relations. Probably not very pretty.
Most likely Nomura got ordered to seduce Kanjigar’s son to used as leverage over him, because changelings are clearly expected to use anything they can to get an advantage. (Changelings Are Not Treated Well, news at ten.) There is a slightly more fun, alternate option that I prefer: Draal, in an attempt to get his dad’s attention, decided to seduce her and figure out Bular’s evil plan, and she went along with it in an attempt to turn it around on him. This would, of course, have quickly devolved into a mutual, very awkward seduce-off as they desperately tried to figure out each other’s secrets and not come down with a case of Forbidden Emotions.
Either way, it was a hot mess of bad flirting, terrible lying, internalized prejudice, manipulation, very obvious leading questions, and self-worth/parental issues. Strickler, an old hand at the whole seduce-and-destroy thing, was always trying to give unhelpful advice. Both of them attempted to subtly win the other over to the opposing side, only to be sabotaged by their own emotional issues and categorical hatred of one another. Draal couldn’t stop accidentally insulting her. Nomura kept contemplating poisoning him. It probably ended in a lot of screaming and a messy hostage situation. Bular and Kanjigar were there, trying to kill each other. Everyone was disappointed in everyone, and no one was happy. At some point post breakup, Draal got his hands on a grit-shaka and they got into a very loud and very personal shouting match/cut-throat duel at midnight in the parking lot behind an antiques dealership.