Jo realized that she might have said that wrong. Probably all of it, though she was okay with being vague enough on the time travel bits. Anything to protect Ellen's existence.
"Someone he slept with before we were together. Not..." she shrugged.
"He knew she was in town and didn't tell me. So I wasn't exactly expecting to run into someone who's seen my boyfriend naked."
Especially considering the fact that she hadn't even seen Dean naked yet.