Its good to have a healthy perspective on our health. But at the same time we can't let it scare us off from living. I agree with Hbollotte. You could be a completely healthy lady, get struck down with brain cancer and die within 6 months. Lots of different senarios play into starting a family. Who knows you could have a child uneffected by Cf if your future SO doesn't have or carry CF. Does that take out the possibility of you dieing while the child is still growing up? No, but thats just something you and your SO have to decide for you personally. ie.could your spouse be a single father. Drugs and therapies are always evolving. Who knows where they will be at when you decide to start a family. Or lets say you get horribly ill 20 years down the road, whose to say what they will have available for you then? Ulimately you make a decision that you yourself and SO can live with. And deal with the rest when you have to!
Its the same senerio if you ever want to get married some day. (I'm assuming your not since your 18 but I could be wrong!) Its the same kinda deal. And I'll tell you the same thing my husband tells me. "He'd never trade the time with me and being married to me for to have never me at all." (kinda worded funny but you get the gist right?) It all comes down to quality of life. He fell in love with me the person, not the disease. And your kids will love you the mommy not the disease. Maybe this helps maybe it doesn't. But me and my husband are totally excited to have kids! Whether its our own or adopted. So do I think its selfish, no. Do we realize the complications that could arise, yes. Its all worth it to us and having a family. And I battled the same things you are right now. With marriage, kids, all of it. Theres no easy answer for ya. Only you can decide whats best. And your docter could be of some help as well!
I'm sure whatever you decide will be fine. Hope this helped a little....good luck!