What happen in the last? Wht they mean i fell in love with him?

I think what they meant is that Mariko fell in love withTakezou.

As far as i understand it .. shinobu (older brother) wrote an apology letter to mariko (his wife). He doesn’t want forgiveness but rather he wants to apologize that’s why he wrote it. And what he meant by “ i fell in love with him” is that he (shinobu) fell inlove with his younger brother (takezou) ., so i do not think that Mariko fell in love with takezou because the one who wrote the letter is Shinobu.

Omg I think your right