I was thinking more on the excuse for the college past, instead of being a literal sucubus, more of a something on her nature made her love sex so much that she couldnt stop herself and that something was some succubus ancestor or some shit like that. A way to justify her decisions to be the campus slut that its not the one that is presented actually in the game (that she just wanted to be and didnt know that she could just say no to mia)
Makes sense. I was just rambling off possible things to be honest. Like you, I was just seeing this as a means for the behavior to be excused/justified which would completely invalidate the MC's position in this. As has already been pointed out numerous times, multiple characters seem to gloss over the MC concerning his objections her past (and present) behavior. They fake pretend to sympathize with him, but then support Lacey in everything she does to hurt him via mild objection, keeping the secret, and so on.
The supernatural insert would just be a "nail in the coffin" so to speak and put the game much closer to traditional NTR stories where the MC is the problem and they are all just innocent people who were driven to their behaviors because of his failure.
As it is now, while the MC does exhibit numerous "traditional" moronic NTR MC behaviors, he does rebel quite a bit openly and forcefully (up to a point where he slides back into the standard NTR role) which allows me to at least see some worth in the story. Well... that and the fact that effort is put to try and "reasonably" explain the various betrayals other than the standard "sex is too good, he doesn't understand me, he didn't live up to my idolized standard, etc... and so deserves soul crushing retaliation".
This also seems to completely invalidate the story setups which try to give off the belief that the FMC is deeply in love with the MC. I don't see how anyone could go from "I completely love you in all that I am" to "You are worthless and weak and I want to see you suffer while I scream in pleasure getting railed by your worst enemy". In that, there was never love at all.
At least with this game, there is some aspect of "love" (regardless if it is healthy or not) between them and it is reasoned in a way that can be "accepted" with some argument.
I would love to see more games like this that focus on the aftermath of cheating. Honestly, I would be interested to see a lot more time on a story where the MC battles with it before and after (as L&J does)and then the story goes on to focus how he will deal with it in various routes (revenge, rehabilitation, FMC regret and stalking, humiliation, etc...).
Though I think that type of story is a very specific type of NTR game? I think I saw some type of name for it, being that the game wasn't about the deadfall complete demoralization itself as an end, but a component of the journey. I am hoping this game even if it doesn't have a "happy ending", it does actually have a "resolution" other than "MC is a loser".