I Will Divorce My Husband for Cheating with My Step-Mother

Leia is the daughter of the Sharon household, and is secretly in love with her servant, Thomas. However, her father, unable to bear his accruing dept, commits suicide. This causes Leia's stepmother to force her into a political marriage. Leia's husband is unexpectedly kind; but just when Leia is starting to have a positive outlook on her newlywed life, she hears an older woman breathing heavily in her husband's room...?!

(Source: MangaPlaza)