I’m so utterly confused

So basically the MC loves her sister so much she'll be willing to ruin her own life just to help her sister. So it's revealed at the end that they are both heirs to the Earl fortune. And the MC did not know until the end of the story and by the end the ML ends the engagement but the MC sister and I think they both are going to get engaged because the ML is quite enchanted by her. ( i'm sorry if it doesn't make so much sense)

THX helped a bunch I was really confused y he ended the engagement and what was revealed that made him