Sometimes friends become more than just friends because the general public “Doesn't get it” and so it’s easier to date within the EMS, Fire, Police or Nursing realm. There are rules, however, and they're in place to keep things a bit less awkward.
The first is that you don’t sleep with a friend’s former girlfriend or boyfriend. That would only strain the more important relationship at hand, but if the friend in question had a one night stand it was, of course, acceptable to hook up with the same person. The second big rule was that you didn’t, under any circumstances, sleep with your partner. You could be best of friends with them, and that sort of thing was more than encouraged, but it was considered extremely taboo to take it farther than that. It made the working environment difficult, and if it ended badly, the crew’s integrity and ability to perform was compromised.
Then there's the most sacred rule of them all; the protocol which must never be broken...