Amattare wa Inu mo Kuwanai
Ongoing | Nitako | 2000 released
One Night Mate
Complete | Cherry Manju, Justice | 2019 released
I think the open minded part was a mistranslation. Since when woojin searched it up on google, the result he got was the same definition with Open relationship. So basically, even if the author did used open minded, it might be the author misused the word,however in the story, it still holds the same meaning as open relationship, at least within the universe of their story
I Picked Up the Second Male Lead After the Ending
Ongoing | Jongso,Hwang Do Tol, 정서,정서 | 2000 released
Ameiro Paradox
Ongoing | natsume isaku | 2010 released
Gokusen