Tough choice because from the tone of your post, you definitely want to go for the fun of it, making your bf happy, plus making a great impression on his dad.
It seems to me that most CFers have pretty dramatically different reactions to climate changes - but in my husband's case, we specifically moved to Tucson, AZ from a very humid climate (Houston, TX) because he thrives in the dry, arid heat. He lived in Tucson on a 'practice run' for 6 weeks while I stayed behind in Houston to make sure it really was good for his health, and it was phenomenal. His hemoptysis is down significantly, his PFTs have stabilized, and he is able to take a MUCH lower daily pain dosage to help him function. Again, different bodies = different reactions to climate change. (he personally does awful in cold, wet weather)
We are careful though about altitude - Tucson is about 2,200 feet above sea level and that seems okay for him, but if we start to do scenic driving up into the mountainous areas, he feels immediate chest tightness and more difficulty breathing.
Whatever you decide, be honest and forthright with your bf - he needs to understand the progressive nature of this disease and realize that he needs to step up in some cases and protect you from potential dangers that he never even realized could affect you.
Best of luck & hope you feel better SOON!