Well why not if it will improve the game ? Jealousy has the power to spice up things and strengthen the desire like when Sarah was story telling about her past,, it's not about giving NTR haters a bit of scare, because I believe there won't be. It's just about adding a thrill but it is up to you
Sure, that's a good argument, I just didn't like the idea of it. It feel like the equivalent of a jump scare in horror movies, it's cheap and is only there to manipulate the player. If I would've done something like that it would have been more intricate, like just as Mark starts to realize Sarah's feelings, she gives up and ends up with a dude how she wants to "use" because she feels lonely. But then she starts to actually date him. All while Mark struggles to come to terms with this weird situation that he's now in.
But this is a completely different story, it wouldn't fit the theme of what I have in mind for future content.
So yes, I understand the appeal of it, I just don't think it would've done well in my game, nor was it ever intended to be included.