I don't actually see that coming at all. I'm usually pretty spot on in picking up those kinda story beats, so if it did happen, it would have to happen in a way that actually breaks MCs character. And considering how well this has been written so far, I doubt that will happen.
The actual sad point rn, is that Adian feels like he is the same as the priest that MC told him about. He separated their sleeping areas, because he feels that he asked MC for his everything, in return for salvation, when MC had nothing to his name. It is incredibly insightful. I actually really love this plot point, because it shows Adian thinking about how his choices, and MCs lack thereof, could have a lasting negative impact on MC.
The reality though, is that the MC willingly made his decision, and hasn't shown to regret it. He willingly accepted being Adians mate in return for the safety of his village. The difference between this situation and the child's situation, is that MC was an adult when making that decision, and adults can consent.
Also, that priest is already dead, but I would personally piss on his grave, and have my dog piss on his grave and teach my kids and grandkids to do so, just so grass, flowers, and bushes never grow there for as long as my bloodline lasts.
Is this gonna have a sad ending.... I feel like uke maybe don't want to be immortal anymore and will later asked to be mortal again and die by seme's hand or something like that. hope I'm just overthink things