Some lessons are important in life - lessons that come through mistakes, suffering, deceit, backstab and going through the cold weather. You need to 'suffer' what you could have avoided - so that you remember that mistake and the lesson learned for your whole life. So, that you understand the impact of the wrong that you have done and what you have suffered due to your own mistake.
Asad believing Zoe at this point ( and that too in absence of concrete proofs ) may save him and Zoe. But it will not teach him what he needs to learn - the shock , trauma and misery that he needs to go through at the betrayal of his best friend will not happen. He needs that pain to evolve into a wiser man.
Let him go through the misery of this backstab if he doesn't read the signs . Its sad because he is a good man and this betrayal will only prove to him that his mistrust in people is right - but it will also teach him that appearances are deceptive and your truth is not always the truth.
I don't wish any deliberate ill to Asad. Definitely not the kind of misery the hateclub keeps saying that he deserves. He maybe opaque and flawed but he has seen enough suffering in his life to deserve any more of it. He just needs to be released and Zoe is that door.