This is the actual story. Get over it. Like I said this whole story/plot is already constructed. So what if Brian's dead? He's a vital part of the story. Take it as going to a therapist. You don't just give a brief history to the therapist for them to truly understand you. For the therapist to completely understand, you will need to elaborate and give a more detail story. The author won't cater to people who wants for Brian's story to already end. They already planned for everything.
Why can't we just respect the author to how they want their story to happen? If they like to be detailed then so be it. Their story, their decision. If the author wants to dedicate the whole arc for Brian, they can do so. If you cannot wait for Ian's return reread from the start or don't read the current updates and just come back if Ian's back. No one's forcing you lot to read the current arc.
I like the reminder at the beginning. Some readers often forgot that not all authors take a short route in explaining and showing the main foundation of a story. When I started this manhwa and noticed that it revolves around political conflicts I knew that it will take so long especially if Ian is a reincarnation of Brian. This current season is basically about how those two met and fell for Brian but it also shows how the two countries are built to what they are in the present. This is a political romance fantasy manhwa. The flashback is going to be long if the author decided to be very detailed.
Remember this; a lot of authors spends days, months even years planning and constructing their plots and characters. They made the story for their satisfaction first before the audience. They want to share their work and ideas that took a long time to construct. This manhwa is a prime example of careful planning of world and character building. Stop complaining about not seeing Ian and how long the backstory is taking. Its already set and planned. The author won't change their story telling style to accomodate readers who have no patience and wants a fast paced story.