Yes its a good ending. They even have a 2nd kid at the end.
Because of their fight in the next chapters, Zigril will want to look for the Mirror of Targo just to see if Kay loves him or not. Long story short Kay does. He just refuses to admit it but because the novel is written in his pov, its pretty damn obvious he loves Zigril lmfao. Tho dont hope for any sort of redemption from Zigril as he is described as a literal monster in the novel. Considering the time+setting of the story, and that zigril was born that way (though he had soften up to Kay throughout their marriage) Zigril will remain the way he is until the end of Mirror of Targo.
As for the 2nd child, it was conceived consensually after the two of them declared their love for each other. Thats what Zigril is trying to buy from merchants. Its also why Zigril asked kay if there's anything he wants in chapter 48.

"Yeah. So much that you couldn’t even say ‘I love you’ as a lie?”
Kay couldn’t answer, and Zigril, smiling faintly, took another half-step back.
A single step’s distance.
Kay felt that step unfamiliar. It was uncomfortable, as if something was caught in his throat.
“You’d better not come closer.”
Zigril stopped Kay, who was about to close that distance. He licked his lips.
“I think I could kill you right now.”
(And fyi, the thought of divorcing zigril makes kay sad. LMFAO.)