I just "happened" across this posting. My "boyfriend-soon-to-be-fiance" does not suffer from cf, but has been dealing with some medical issues as of late. Thank god everything is OK :)
However, I also had some serious lack-of-support issues coming from my dad and his side of the family. Mom has been very supportive. His side of the family said... "Don't leave someone when he is sick, but as soon as he is better, you should get out." This is a very difficult decision when you love someone, and very hard to hear from the people you love.
The point is, you are who you are, and your mom is who she is. If she is open to counseling, I say go for it. Unfortunately, though, you have to make the tough decisions about your life, whether mom likes it or not. It isn't easy, so I sympathize with you on that, but it is what it is.
Good luck! I wish you and your boyfriend lots of happiness :)