What's wrong with me?

Maybe they need to be informed about the disease and what it actually is so they know that it can't affect them and it doesn't affect you going out with someone. When people are unsure about something they just run from it, so let them know what Cystic Fibrosis actually is and they might become more comfortable around you. Or maybe they are telling the truth and they do actually have a boyfriend or they just want to be friends with you, who knows?