Marl is just jealous again, and wanting to keep the MC all to herself, no matter who she has to drug and rape to do so. She's jealous that that blond knight Waltz is better looking than she is, and a better adventurer, and a better kisser. Then the MC goes and gets proposed to by that nobleman when he gave the MC that shortsword. The MC accepted, so he's basically engaged to that viscount now. Her petty pride as a princess is warring against her petulance that made her run away, so she can't handle how she's losing her favourite toy to the lure of BL.