Wanting MC to do party planning with her is meant to be a sign of the growth of their relationship. If you recall, it's what Sage wanted Chad to do with her in the flashback (though Chad didn't care!) In fact, despite Sage's absurd claim that she's "never seen the MC that way" DPC has made it increasingly plain that she has developed feelings for him. She's opened up to him about her emotional issues, been moved to tears by the story about his mother, calls him a "great guy" to other people, kisses him in public, thinks he's great in bed, wears his jacket etc etc etc. This is all a bit beyond him being a toy, surely?