Aaliya friendship with Zubbu has nothing to do wit Zain's. I mean what logic does it hold that since Aaliya trusts her friend so he should do same. Episode was illogical enough coz there were no proofs as such to make Zubbu even a primary suspect. Watch was found near lift well every person uses lift so it cld hv fallen and entering into Hotel well that was another stupidity
Zain is going through emotional trauma, his father who was world to him, his support system who always held him is dependent on others for support. He has brought his father back from death bed so how do u expect him to think or act rationally. And slap was a sudden action by Suraiyya when all were beyond shocked that Zubbu could do such a thing.
Give them time to at least ponder over things again