That fucker. First he goes "You're unpleasant to look at." and now he's upset and crying that she left him? WTF. He just feels sorry for himself when he realized what he lost. Even if he didn't know how the society behaved towards her... which I think is kinda bullshit, those remarks were probably flying around a lot for a long time... IT GIVES HIM NO EXCUSE! You were living together for 10 years, or at least 7, when we count that he was in war for 3 years! Ugh! I am so happy she left him!
I know how everyone talks about how they find it gross that they are siblings... but I really can't see any sibling behavior/feelings between them? They were practically strangers at the start (see how she's constantly surprised by his behavior?) that called each other "brother/sister". And as it was said, noonim can be used generally for older women, not only sisters. Not once they behaved like siblings for me. So I don't see your problem. (I don't want to sound rude, I just don't understand. I have younger brother and I can't see the connection I have with him in Ran and Yusuf.)
There are other stories with step-siblings relationships that are waaaaay stranger, mainly because those people often grew up with each other or gained siblings through their parrents marriage later and wanted siblings, tried to view them as siblings from the start. But Ran viewed Yusuf as ML of the story, as an important person she wanted to help right from the start. So I really can't see them as siblings. She can't even agree she sees him only as her brother in the chapter!