This is why it's a bit disappointing that DPC won't bring on some help because sometimes having a 2nd opinion, particularly one you respect, can often help in these situations as writing is very often collaborative. Even for solo authors, they will often go to respected friends and colleagues to ask their opinions on what they're doing with their story, but DPC seemingly does not, and this can also help as this other person could remember details that the author doesn't because they're so immersed in what's coming next that they've forgotten some of what came before.
Aside from this being a clear sign Tybalt's lying he doesn't want her talking to this other Prep, it is disappointing that she just ends it there because as soon as Tybalt tells her to stop seeing him, which happens off screen, she could have then put her foot down by saying that she won't and if he (Tybalt) suggests that she'll never speak to him or maybe even move out. However, as I've been saying, DPC has made Jill too meek to do this and it's led to this annoying situation.
I don't look forward to this decision and also don't like the idea of it, but I'm also concerned that, by being on the M&J path, that this won't even be a choice and I really don't want to see anything bad happen to Quinn just for choosing one particular relationship.
It's possible, because if it were to ever get back to Derek (not sure how that would happen) that he laid all the blame at his feet, it would certainly not put him in good standing with Derek, the DIKs, and especially Maya that he would throw him under the bus like that.
Just use the mod on a copy of the game and change the variable to make it so that he had the threesome with R&Q then do that M&J scene and it will unlock the remaining 50%.