She played him like a violin. It's good in a way sinc etheir relationship advanced, but a person that is fine with lying to and manipulating their loved one is a big red warning for me.
The main character dude really is a dumb little bitch sometimes, isn't he? First either threatening to resign or making a high school girl who he's barely dated marry him and then when it turns out to be a prank he throws this juvenile tantrum. Jeez.
He was a dumbass for leaping to the "let's get married" thing, but SHE was an even bigger dumbass when trying to prank him about something as serious about that.