Aiden is Catherine's bf. Its been stated its you NTRing him. That got cleaned up a bit in the 0.8 version as some misunderstood it as MC being at risk of being on the losing end, when it was MC about to cuck Aiden (taking Catherine).Yeah he should give first priority to his paying customers, but the walkthrough mod said netori route for the mc showing Steph's pic to the other kid, which was what confused me, then he shows his girlfriends bottom to aden, which was a nice scene but Aden is a innocent kid.
The premise being Stephanie and Catherine have relatively similar bodies, and MC being sadistic (Catherine Corruption route) in wanting to have his way with her and getting to laugh as Aiden would be cucked to his face in a way that he would likely be unaware.