She slept with my ex didn't mean anything, not really, and it certainly wasn't worth the pang in his chest for something Rebekah had done before he met her. The thing was, it meant that Caroline and Rebekah had traveled in the same circle long enough for Rebekah not only to sleep with Caroline's ex but for Caroline to know about it. Couple that with the alcohol and the fact Rebekah had steadfastly not mentioned Caroline, it gave Sam pause.

"I think she felt safe with me. Like she could stop worrying about being an Original and just be Rebekah." There. If Caroline knew the world, she'd know he knew and know what he knew. If she didn't, then she probably wasn't a vampire and it was just an odd turn of phrase.