Hello!
I can't say how everyone is going to react, but it has been my experience that honestly, it has not really affected much. That sounds funny, but all of my friends are really supportive, and they come visit me whenever I'm in the hospital and they even go on the CF walks with me, etc. Also, for what it's worth, I was upfront with my boyfriend and he has been a total sweetheart. He's even gone to the doctors with me, and been with me while I do my PFTs and IVs.
I agree with angelofshadows that if they don't accept you because you have CF then, honestly, you don't need them in your life anyway.
That goes for me too, that if you have any questions or just ever want to talk, feel free to PM me!