Your post sounds like you are absolutely stuck in your situation, a daughter with MS.......how could anyone make her fend for herself? Sad that you had to take on the boyfriend too but I trust your judgement about that situation.
I have just one question.....What are you doing for yourself? You are taking care of everyone else (even the boyfriend) but are you taking care of yourself? I tended to put everyone else's needs and desires before my own. As mothers we are actually programmed to do this. The entire time we are raising children it is very important to put their needs first but lets face it, my kids are grown. Their happiness is their responsibility and comes as a direct result from their decisions since they stopped listening to me. I now live by a couple of sayings......
1) What you focus on expands! (So I try to keep my focus on the good things in my life....it works!)
2) No news is good news! (So I stopped worrying about what they were doing/thinking/blaming me for)
3) Not my circus, not my monkeys (a reminder that I could not "fix" their problems, they had to)
My life has changed in marvelous ways since I started using this approach. I know that you have your DD living with you but I feel certain you could employ at least a little of this method. Good luck!!