I can empathize with you. I am not yet close to transplant, but I get sick on a very specific cycle of every three/four months. It leaves me very little time to pick up the pieces of my social life. I have not yet solved that problem, but use my 'good' time to pursue things I like to do. If my friends are still around, they join me, but not many are able to understand the rigorously scheduled, un-fun CF life. Whatever. I can see things from their perspective and understand how it might not be awesome hanging around a sick lady who has to be home early, can't drink, and has a weird restrictive diet (CFRD) all the time. I guess I just made peace with that and don't worry about it too much. When I stopped working I had a lot of identity issues about who I was without a job; I got used to it, too. I think of CF as a job, and I don't feel guilty about other people's misperceptions of my situation.
Unlike you, my parents only help out financially in smaller ways, like occasional groceries or clothes. It's probably because I'm married that they don't help more, but my hubby and I are pretty destitute since I don't qualify for SSDI. If I were you I would gratefully accept my parents' willingness to help, knowing that if I could, I would do exactly the same for them. I don't know why in our culture we are made to feel like we should be totally independent of each other; it's a sham. We will all be dependent on each other at some point, we shouldn't be made to feel ashamed or guilty about it. Our culture makes weakness into a vice, wants illness to hide itself (unless it's got a great, hyper-positive PR campaign like breast cancer does), and considers us valuable according to our ability to work. Think of the older Americans who are shoved into assisted living facilities because their children consider them to be too needy and disruptive of their own lives (or whatever their reasons are for doing that). I wouldn't do that to my parents, no matter how strained our relationship sometimes is. Sorry, I just stuck a rant in here. My point is, it's okay to be weak, it's okay to need help, don't feel bad. It's clear your parents love you and want to help you. Let them, and relax your conscience about it.