Sick Kids in Love By Hannah Moskowitz.
"Isabel has one rule: no dating. It's easier-it's safer-it's better-for the other person. She's got issues. She's got secrets. She's got rheumatoid arthritis. But then she meets another sick kid. He's got a chronic illness Isabel's never heard of, something she can't even pronounce. He understands what it means to be sick. He understands her more than her healthy friends. He understands her more than her own father, who's a doctor. He's gorgeous, fun, and foul-mouthed. And totally into her. Isabel has one rule: no dating. It's complicated-it's dangerous - it's never felt better - to consider breaking that rule for him."-- Dust jacket.