100-Nichi Go ni Fukushuu Suru Sare Tsuma

Yuzuki and Kosuke, who married after three years of dating, are a couple that everyone acknowledges as being very close.
However, one day, Yuzuki receives a message from Kosuke thanking her for a lunchbox she doesn't remember making, and shocking secrets about his life—office affairs, baby play, and a secret social media account—are revealed one after another.
There's a husband she doesn't know about on her smartphone.
Amidst all this, a message arrives on social media asking, "Would you like to take revenge with me?" Spurred on by this, Yuzuki changes her account name to "The Cheated Wife Who Will Take Revenge in 100 Days" and vows to take revenge over 100 days.

Original Webtoon