My Husband Ry had CF, and I know what you're going through right now. All the doubts that are slipping into your head, all the worries that someone your age in love should never ever have to think about. If I had it to do over again, I would take that leap in a heartbeat or less. It's the constant arguement of passion vs. safety. Wouls you take 5 years with someone you love with everything in you, or 50 years with someone you can tolerate?
All you can do is hang on, and love as much and as strongly as you can. In my experience, you'd be surprised at the thousand fold love you get in return. The future holds nothing you want to see. Hold on to the magic of today, and let the future take care of itself.