Feels like both mc and the prince has very many options to take which they aren't. ie. prince still favors villainess, and made her fall in love with how he acts to make her happy, but is clearly not acting to make her happy in those chapters. I can give him a pass for now tho, as it can be him thinking she tries to befriend the commoner girl to secure human resources, or even just him seeing mc jealous and enjoying it.
But the mc is clearly not acting reasonable, aside from all the possible actions she can take based on knowing the plot, she could also easily just not play along to the script and instead reprimand her for "intruding on their date". Even if she doesn't do that, she could "confide" in felix that she wants their time alone, and ask him to help her extricate themselves during those moments when the girl is being pushy. She could also ask the girl (with felix hearing) to simply stop stalking mc as mc's "friend", if she is going to be trying to seduce her fiancee in front of mc. And that if she accuses mc for her breaking her own pen, then she should remain at distance before ppl start gossiping blame on mc for whatever other incidents she has planned. (the last sentence might be better to say when she is unaware that felix hears them, to bait her).