I'm not sure if I should point these two image out to you or not, since it might put you over the edge...
I'm shocked you didn't pull out these smoking guns...
Just have to wait and see.
However, based on all available information, Julia has not cheated on the 0 corruption/trust/faithful route.
This would be a very long "con" when she could have done it the night before and not traveled all the way out to wherever with Cornell's mom just to "do it"... And if anyone was going to "mess" with the MC or reader in that moment, it would have been Jasmine. Jasmine's convo is the story's way of telling you, relax, she's not cheating. Now, if Jasmine had said something "provocative" in that moment, you might have a stronger argument.
I will concede to you, the contrived "plot"/story is definitely forcing the mistrust, jealousy and suspicion on the reader/MC.
And it's not completely out of the realm of possibility that Julia cheated on that "trip". (Have to wait and see)
There's just not enough to support a reasonable suspicion and it would be completely "out of character" for Julia (and the dev) to act on her own accord with 0 corruption when at much higher corruption, she's loyal when she doesn't have to be.
I hate doing a body language analysis on a fictional character render...lol
But in the drive-in scenes, Julia is showing affection to MC she is not showing Cornell, and Julia shows little to no signs of regret or guilt for having cheated.
She does show the signs of curiosity, what-if fantasizing, feeding MCs lust and jealousy, maybe even a little bit of "stockholm syndrome" after having played the fiancée all that time and "alone" with Cornell and his mom that day... But physical cheating, no.
I know none of this is going to change your mind...lol
I doubt even if the next update came straight out and said nothing happened, you wouldn't be convinced unless there was drone and CCTV surveillance of that entire day and all of their interactions...lol
Just gonna have to wait and see.
Relax, deep breath, maybe have a drink, and take a break from NTR games for a while, they're stressing you out...