Yeah I've always wondered as well and I read this a while ago and it makes the most sense to me. "Makes me wanna blow the candles out just to see if you glow in the dark-this can mean he wants to see if she is actually that special after all this. does she glow in the dark, does she revel, even through the eye of the storm.

The Shalalala can be the protagonist trying not to pay attention to what’s obviously in front of him. After her revelation, he still wants to see if she’s special and the shalalalas is him sort of behaving like a child when they go “la la la la la la.” He puts his thinking cap on and sees she’s got a telescopic hallelujah but he doesn’t care too much, he still wants to ignore it so he goes shalalala. Even when he realizes she’s done the devil’s pedicure, he’s like fuck it, sing another shalalala.

So in the end, he doesn’t end up leaving. He’s still singing shalalala in the end, ignoring all of her faults."

Credit to: drah22692 from genius.com