I dunno wtf is going on. I mean I've seen some "NTR" oversensitivity before but this takes the cake, because in effect you are cheating with yourself, since both MC's are you. With a lot of AVNs the NTR is optional, esp with multiple protags where you control LI actions as well. Don't want that to happen then make them not cheat, simple. This is not much different, as there's a choice to not open her path with Cabin MC if you don't want her to fuck him too, so I dunno what the problem is. I mean are there unknown future plans only they are privy to to simply have her fuck some other yet-unintroduced dude if MC here turns her down? I seriously doubt that.
Given how crazy this site can be just as a joke and psychological experiment I'm tempted to make an AVN not for money but as a joke and psychological experiemnt see how many people here I can make fall in love with the main LI in it in 6 updates, and then in the 7th and grand finale not only have her cheat on the MC multiple times but also have her gang-raped, tortured and killed while the MC watches before the same is done to him just to see how many former readers get depressed and kill themselves in real life.