Well we all know the ex is a manipulative, materialist, selfish person. What's more interesting is our MC's reaction, and how he will deal with his reaction. He's pretty clearly shaken to see her. And within the last 24 hours he got confessed to, by his oshi, who is much younger than him; He's already in an emotionally confused place. And the manipulator knows to go for the throat by calling out the younger woman at his place, even though that's not what she came to do. It's just an easy opportunity to weaken him before she asks for what she really wants.
So what will he do? I hope this cliffhanger has him standing his ground and telling his ex to take a hike. I hope he manages to tell her she's terrible to him and he wants nothing to do with her.