I know what you're going thru, because I used to be the same way. I felt if I said "no" that people wouldn't like me anymore. I felt that they'd never talk to me anymore if I said 'no."
My therapist told me that I couldn't be walked on anymore if I didn't lay down.

And she was right. So I did like the other posters said -- I started saying "no' to small things, like when they asked to borrow things, or rides, or wanted me to babysit. Pretty soon, it wasn't so hard anymore to say NO. And no long after, they quit asking me too!

The funny part is, even if you DO lose "friends" like that, you find out that you really don't MISS them at all! They were only your friends due to what you could do for THEM!
Practice saying no. It might be hard the first few times, and you might even get anxious about it. But that will pass.

And you WILL be better off for it. God bless and please take care of YOU. Hugs, Lee