Hi,
I just though I'd share my experience with ya, since its a little similar.
When I began dating my now husband, back in 2000 I had no idea his son had CF. He didn't tell me, and I don't know why till this day. But, I found out through his roommate who was just as shocked as me, it seems my husbands Mother called to see how he was doing and my husband wasn't there so his roommate answered and talked to her. When she said she was concerned about her grandson and his breathing problems he was confused which led to her explaining the disease. Once he found out he asked if I knew, which I didn't. I was really upset that he didn't trust me enough to tell me about it. We had been dating for about 6 months at this time and I have a son from a previous marriage which is the same age as his. I don't know till this day why he kept it from me. Maybe he thought I would look at him differently or something. But since we have been marriage he has learned how to open up a whole lot. He talks with friends about it and is very open when it comes to his sons disease.
Now, we have been married for 3 years and I've learned so much in this time period. Just like you mentioned about your friends son, you could not tell anything is wrong with him if you just met him. But, he does have problems and I have learned so much about this disease in the past 3 years. But please keep in mind, if you and your friend become serious one day, you should think seriously about genetic counseling before having any children. It never occured to me that my husband and I could have a child with CF, but when I became pregnant with our daughter I decided to get tested and found out I was a carrier. It was a major shock. That meant my baby had a 1 in 4 chance of having CF. After a long terrible wait and amnio testing we discovered my daughter is a carrier like us but she does not have CF. I am now pregnant again, and going though the same nightmare. So, please consider being tested before deciding on having a baby with a known CF carrier.
Jen