Felix really doesn't want to hear the explanation, and yet if he knew there was a recurring partner he might have to fight off the urge to go duel them for reasons he couldn't fathom. But he doesn't know that (yet, anyway), so all he has to react to here is...

...Dimitri just outright saying things like that. Even after Fhirdiad, when they started occasionally having actual conversations that didn't always devolve into arguments, the king Felix knows has yet to say anything like that aloud. It's not like Felix is unaware that Dimitri cares about him. Felix might, if he were very drunk or on his deathbed, maybe admit to caring about Dimitri, too. They just don't talk about it.

"...fine. Do as you please. But don't expect gratitude for something I didn't ask for."

He glances over with raised eyebrows. "Parley? Huh. Bold move. ...I hope it works." It's not as surprising to him that they managed to take the impenetrable fortress as it might have been a few weeks ago, from Felix's perspective; the addition of the entire Leicester force to their own will undoubtedly make a big difference.

At the mention of Edelgard, Felix quickly looks away again; the look on his face is definitely not sulking, thank you. "...I know. I already...encountered Edelgard."