Shawn Spencer is a go-with-the-flow kind of guy. So when Lassiter misinterprets one of his visions/antics as a come-on and accepts, he goes with the flow. And he's used to relationships collapsing, getting dumped after a few weeks; so much so, that he's extremely confused when Lassiter doesn't break up with him, and doesn't break up with him, and doesn't break up with him...until Shawn finally gets used to it. And then he does. And Shawn has to figure out how to win him back, when he's only just realized what he had.