I’ve given this quite a bit of thought and have been ambivalent in my lamentations. The demon Malphas possessed Ayushan and not Zoltun. Demon’s are a concept with prevalence in all Abrahamic religions. Muslims have the djin, which we call genies, and Jews have the dibbuk. In all Abrahamic religions demons posess a person through weakness and temptation.
As far as I can tell, the Mythos in Diablo has no position on same sex attraction or same sex relationships unlike the Abrahamic religions that underpin said mythos. While there have been same sex characters, we dont know whether the church has a position one way or the other.
I bring this up because theologians believe(d) that a demon would trick a person into homosexuality as part of their mission to corrupt souls. If this same belief is held by the church in the game, then Ayushans attraction to Zoltun would have been the catharsis for his possession by Malphas.
At this point I should clarify that I am not professing an opinion on homosexuality. I’m only referencing a bit of theological history as it applies to demonic posession and a presumption of attraction between two male characters.
Zoltun is an egotist and also brilliant and he exhibits all the behaviors of someone with Psychopathy. As such he would have leveraged Ayushans attraction to manipulate him. Due to the characteristics of someone with Psychopathy it’s very likely Zoltun’s soul was already damned, and he’d be smart enough to know it.
Psychopaths are incapable of meaningful emotional attachment to others. As such Zoltun’s likelihood of engaging in a loving romantic relationship impossible for any purpose other than manipulation. It’d also make him far harder to possess as Malphas would have to out smart him and do so long enough to wear him down.
Early in the story theres a note you can optionally find where Zoltun writes a missive about Ayushan running out at night and forgetting to arm the traps. This is where Ayushan was possessed as his own recollection is that he was still working with Zoltun.
The story also provides that there was a significant period of time between the completion of the Loom and the possession of Ayushan. So the celebration was not what triggered the attraction of Malphas, the energy from the Loom was.
I think Ayushan had a love/hate relationship with Zoltun. I think if anything he may have had an attraction to Zoltun he either was unaware of or lacked faculties to understand. I also believe Zoltun realized it and used it to his benefit, ultimately leading to emotional turmoil for Ayushan. That turmoil was played upon by Malphas and used to weaken him for possession.