Fake Affair

Both have a person that is sick and may die that leads to the female and male leads jumping into a relationship.
In SMH- The male lead's mother is diagnosed with cancer and is worried about her son being alone after she dies. So her son jumps into a marriage after only meeting his bride to be one time. The female lead caught her boyfriend cheating on her and decided she wanted to be married to just someone because she wants to escape her parents house and her current life. She meets the male lead through a dating app and they decide to marry without knowing each other.

In GF- the male lead has a brain tumor and is terminal without doing a risky surgery that could result in his death, So he comes to Japan to do some things before he dies. One of those things is he wants to fall in love one last time. He decides to look for someone he can have an affair with so when he dies the girl wouldn't be alone she'd have her husband to support her, He meets the female lead on vacation who is single but she lies and says she married. thus the affair begins. The female lead is attracted to the male lead but she lies about her status because she has tried unsuccessfully to date for years and has been told she is boring ,so on a whim she says she's married.s