This is a mess. Several flashbacks of different length without clear boundaries already made the start bumpy but now there are 2 Chapters of individual backstory in a weird/unnatural narative.
The FL has not spoken a single word in present time which makes her seem daft (I mean seriously even if you know they don't understand you, showing that you speak a different language and trying to communicate SOMETHING would be helpful).
The ML called her "foreigner" in the very beginning but doesn't realize she speaks a different language for sure, come on?
And given he was already kicked out and never really was attached to the church it makes no sense why he is so hung up on that oath to mention it several times (all in all it seems like almost everything gets repeated over and over, we got it the first time thank you, moving on)
What is his stepmother going to do afterwards, just kicking him out is not going to solve the inheritance issue - a lackluster, cliched and totally not thought through backstory. Same for FL if her mom got pregnant against her will from a one night stand there exists something called abortion and the question plus answer about the dad also seem completely surreal.
Well this may come off as really harsh after all, but I was really expecting more of the story given the intro