You Shine in the Moonlit Night

Takasaka Aoi lived happily with his wife, Mitsuki, and their son Ren. But one day, during a medical examination, he was told he had only three months to live. Encouraged by his beloved wife, Aoi decided to fight the disease. But when Aoi left, Mitsuki took out her smartphone and made a call. "Ken-chan. Aoi-kun is really going to die!" Mitsuki's true nature gradually becomes clear. With only three months to spare, Aoi must uncover Mitsuki's true identity in order to protect Ren!

After receiving a terminal diagnosis, a devoted husband discovers his wife’s affair. With little time left and his son’s future at stake, he embarks on a relentless quest for revenge that will change their family forever.

Both have ill female leads, but in You Shine in the Moonlit Night the FL has always know about her condition.
The leads both meet by a coincidence so to speak.
You Shine in the Moonlit Night focuses more on the ML doing his best to be there for the FL, and was a very sweet young romance story.

Min Su, a playboy who believes there's no true love, can't stand long-term relationships. However, the fate takes him to a dazzling beauty, Hye Won, who just escaped from the boring hospital. She leaves a strong impression on Min Su. Again, chased by a nurse, as Hye Won sneaks into the men's room at the hospital, their 2nd encounter is made. And Min Su gets totally captivated by this bold lady, although Hye Won tries to resist him worrying that their love might expire soon due to her terminal disease.