Well, that answered that. Thing was Faith wasn't going to be ashamed of it or hide anything. In her mind if Dean should have been keeping it in his pants while they had fun together it was better Jo find out about it now and ditch the punk.
"Yeah, I saw it. Had his shirt off and all that so it was kind of plain as day." She shrugged for the thanks. "Whatever, it's my job. Vampires...slaying...great job, crappy benefits and absolutely no pay."