Can we talk about Blaine’s face here for a moment?
Through the haze of alcohol, he’s already regretting what he’s done and feels absolutely disgusted with himself. He’s already thinking that he’s screwed everything up and he has no idea how to react or what to say.
He makes the choice to leave the situation instead of getting back into the vehicle. But I think the ultimate reason he decided to walk away was because of how ashamed he felt for putting Kurt in the position that he did.