Varkas still acted as the Grand Duke at first, since their place was also in a devastating state because of the war, this was like somehow his distraction. He didn't eat properly, he had easily became someone who became like a prisoner who did not eat properly and was abused (that was what the Healer said to him when he woke up after he passed out for 2 days because of his state).
Moreover, he did not see any color anymore, he was like a hollow person. Since the one who let him saw color was through Thalia, yet now Thalia's gone, the color of his world also faded.

Edited
DAMN I JUST READ THE LATEST TRANSLATED NOVEL OF THIS HAAA
SPOILER AAAALEEEEEERRRRTTTTTT
This is somehow kind of refreshing, what's happening to Thalia later in novel is kind of heavy to read. From being hated by his family and vassals, to losing their child, being accused of being part of pagans, her ACCIDENTALLY(?) poisoned him with the most dangerous poison(made him almost die), knowing her husband had killed a Magical Wolf who she think their reborn child (so she lost her child twice ) AAAAAAAAAA THE 3RD ARC IS ALWAYS IN VARKAS POV, I WANT TO KNOW HER SIDE IN THESE SHINANIGANS THAT HAPPENED TO HER AND OH, To remind you they haven't had a SINGLE TALK ABOUT THESE INCIDENTS AT ALL. NO PROPER COMMUNICATION, JUST TIME PASSING BY These things happened in the span of 3 yrs. Imagine being depressed to becoming okay again then very depressed again then becoming happy then very depressed AGAIN LIKE A CYCLE ALWAYS FOR THE FL, I cannot fathom how she handled all of these.
Although these things happened to her, Varkas protected her in his own ways. Which made things not to go worse than she had experienced. (But damn THINGS is still very BAD)
EDIT: The latest novel now is at 236, the last chapter I read was 224. I AM NOT PREPARED TO READ.
VEEEERRYY SPOILER AAAALEEERRRTT
I havent read but I got also spoiled that THALIA had DIED. WWWWTTTTFFFFF