I also think it's not an open/ambiguous ending! Why? Because Yuka actually never submitted the divorce paper!…
The subs from KissAsian say "divorce paper", but she actually says "wedding paper" (idrk how to call it xD). She actually turned the divorce paper in, so it was hard for them to say, that they want get married AGAIN!
That's the first link you can find on google! Hope it helps you a bit :)
That's the link of the manga!
I don't know if you can read Japanese or if it helps you, but yea... Here you go!
She actually turned the divorce paper in, so it was hard for them to say, that they want get married AGAIN!