sugar rusher
a guy who's super sweet and hyped on you at first and then without warning his interest dies. It feels like a sugar rush but in reality, like a 'sugar rush', it was never real and all in his mind to begin with. (because scientifically consuming a high level of sugar does not increase hyperactivity in the brain.)
Jeremy used to text me everyday a few weeks ago when we met and now he hardly says anything to me, I think he's a sugar rusher.