Ever since Peter took Madison home to meet his parents on their first one-on-one, the two have inarguably had one of the strongest relationships on his Bachelor season. However, she's been holding back an important aspect of her life that may throw a wrench into their future together. In fact, Madison may even leave The Bachelor and remove herself from the competition entirely, if the promo for Monday night's overnight dates is accurate.
As Madison told her mom during her hometown date, she hasn't yet told Peter that she's waiting until marriage to have sex. This could pose an issue for her and Peter — not because he won't be respectful of her decision, but because it simply may not align with his own values. Not only have the two already determined that they have different relationships with their faith, but Peter has made clear that physical intimacy is important to him, and it's obvious from all his heavy onscreen makeouts that he's a quite sexual person. Ultimately, he and Madison just may not be on the same page when it comes to what they're looking for in a long-term partner.
And even if it's a not a dealbreaker, Madison may have told Peter too late: In a preview for her fantasy suite, she tells him that she "wouldn't be able to move forward" if he's slept with the other remaining women. Peter responds, "I have been intimate. I can't lie to you about that." Visibly upset, Madison then walks away from the table.
Now, this doesn't confirm anything one way or another, but it would support a popular Bachelor theory that Madison leaves and then Peter chases after her, similar to what Colton did with Cassie. That could explain his mom's "bring her back" speech we've seen teased so much, as well as why Peter seems to think his ending is so un-spoilable; it's not a conventional finale.
Then again, Bachelor promos are known for being misleading, so it's just as likely that Madisons opts to stay even after having this difficult conversation. But right now, all the evidence is pointing to her quitting the show.