He knew that you had feelings for him, of course, how could he not realize? It was amusing to him, seeing you try to hide those feelings. But Millie was also an asshole.

So when someone revealed their feelings for him. He flirted with them in front of you. When the person finally left, Millie looked at you.

“What’s wrong? You look like you saw a ghost.”, he smirked at you as he sat in his chair, wondering if you'd admit your feelings or keep quiet like always.