This is another item that has been debunked in later seasons, but Sam had a very bad track record there for a while. One that was even painfully eluded to by Charlie in season eight's "Pac-Man Fever" and even in a faint way by Dean in last season's "Baby."
Charlie: Sorry you had zero luck with the ladies.
You've got to admit, it's a pretty poor track record. Jessica, Madison, Ruby, Annie, the five ladies that were turned into an Arachnes in "Unforgiven" because Sam slept with them (and very likely killed by hunters by now), and even season one love interest Sarah Blake met her demise, even though Sam technically never slept with her. But a few people are still alive...maybe.
There's Dr. Cara Roberts from season four's "Sex and Violence," but I've always maintained that she's really dead thanks to a bizarre gardening accident. I dare someone to prove otherwise. Amelia is probably still alive, but honestly, wasn't she kind of dead anyway? She and Sam had zero chemistry. The hooker from "The Third Man" doesn't count because it was a business transaction. I imagine Sam's quick flings though from "Clap Your Hands If You Believe" and "Baby" are probably still alive, but they should be very, very worried.