I was quite suprised because I thought only his Ammi would be Sahir's softpoint, but it seems like Zaki is one too.
The whole scene where Zaki apologised and Sahir ran after him was just beautiful. Part of it was funny and part of it was very emotional. I have the feeling that this defines their relationship. Zaki can joke around with him (within limits) and sometimes Sahir is really angry at the stupid things his younger brother does but at the end of the day everything is fine because they love eachother.
A very important part of the scene (imo) was that Zaki couldn't swear by Sahir's live (because he knew the swear was a lie) but had no problem to swear on his own live, but seeing this Sahir imediatly hinders him. They love eachother more than themselves and I wonder if this will also be shown when/if both of them fall in love with Arzoo...