I have a theory that is when xie yan meet ge yi in the blissful temple arc, he actually suspicious of mc disguise because ge haiyu is never compassionate or close with his father in the first place. So I think ge yi is shocked that his son is dead and doesn't want revenge but his regret holds him back that is he did not bond with his son in the past. So I think he is in denial but he doesn't want to miss the chance to bond with ge haiyu(xie yan) even though he doesn't know whether it is his real son or not. 

So ge yi sa gambling addict and a Major Self-Gaslighter

Other theory: Ge yi actually know his son is dead and just want to observe mc's actions