Plain and simply, I tell people right away. They are obviously going to have lots of questions (refer them to this site if can't answer all of them) but if it is something they are unable to deal with the first off they don't deserve you because you're awesome, and second you won't get your heart broken later. I just went through a horrible break up (it had nothing to do with CF) and it's not worth being broken up over something that's out of your control.