Hiya! I am a CF female but I have a brother with CF who is starting to think about having a family with his partner, so I have been reading a bit about it and will try to answer as best as I can. I might not get it completely correct though, hopefully one of the wives/girlfriends of CF guys on here may help out too!
A small percentage of CF men are not sterile but the majority are. The reason for this is that there is a blockage in the tubes that carry the sperm from the testicles (where it is made). This means that although CF men produce sperm, when they ejaculate it doesn't come out. With me so far?!
There is a technique now available called ICSI which has enabled CF men to father children. It involves the father's sperm being removed from the testicles (with a needle and syringe), injected into the mother's egg under a microscope, and then the fertilised egg is placed back in the mother's body.
Like other techniques like IVF, it can take a lot of attempts for this procedure to work and result in a pregnancy. However I have heard of a few CF men who are now very proud fathers so it is possible. The best place to start in getting information would be your boyfriend's CF consultant. Hope that helps a bit!