Cathy, I get a feeling from your words that you aren't quite ready to say, "ENouGH cool!" Something within you is making you keep this as a 'need' and as a friend. You will have to say to yourself, (to borrow and revamp Josie's words): that YOU can matter to YOU and that is not a selfish way to be. YOU can be kind to YOURself, and have a life making YOU smile. To that I add, you are worthy! It's a matter of claiming it. It's a matter of believing it. It's a matter of caring enough about yourself to take it.
This does not mean you need to go as far as being unkind to those who are depending on you being an intermediary or their primary support. Quite the contrary. With the new found you, they will learn to respect you more, but for many more reasons. I know this from experience. I've recently (as in this very year) found my backbone and my voice (PTL!). And, I'm not turning back, ever! I wish the same for you... you simply must find it in yourself to find and be YOU.... you aren't truly at your maximum potential and of maximum help to any of those who lean on you until you do...this being because of the potential resentment you hold when you're 'in the middle.' Good luck.
I want to say more, explain more, but my screen is jumping - such agravation --- and the reason I don't participate @ BWS!