Kaitlyn Bristowe opened quite a Pandora’s ‘box’ on Monday’s episode of The Bachelorette by having sex with contestant and walk-on Nick Viall. It is not clear yet if the guys know exactly what happened but they know something happened. Shawn Booth was so upset when Nick stayed the night with Kaitlyn in Ireland that he went to producers and told them Kaitlyn had already told him he was “the one”.
He and Shawn are roomies in Ireland I guess and Ben H. could tell that she had done something to give him “some type of validation.” So it sounds like from her conversation with Ben Higgins that he knows she told Shawn he was “the one” because Ben feels compelled to confront Kaitlyn about whether he is just “spinning his wheels” by being there. 
Ben says he went to take a shower and when he came back things had changed. I suspect Shawn had just returned from talking to Kaitlyn. I also suspect both guys know she slept with Nick and are understandably upset and considering walking off.