Worst. Bachelor. Ever. (And yes, we’re including Juan Pablo Galavis!) The Bachelor’s Arie Luyendyk Jr. proposed to Becca Kufrin, then dumped her for runner-up Lauren Burnham while cameras were rolling — and now she’s telling friends all about the unforgivable act. “Becca was completely blindsided,” a source tells In Touch. “Arie told her he loved her multiple times a day. Little did she know he was going to betray her.” Arie, 36, reportedly didn’t even give Becca, 27, a heads-up, letting her believe that they were filming a “Where are they now?” segment. And while he claimed that his decision had nothing to do with Lauren, 26, Arie had actually already spoken with her to confirm that she’d give him another chance! Even worse? “Other people knew before Becca did,”…