I've been in the position where I was asking for things that I needed people to say "no" to if I ever wanted to get better. As the "asker", at the time it hurt to hear that word. I felt like I was being abandoned and that no one really understood me. Two years and two months later, I realize that those people love me and were trying to help me.
So the challenge is to figure out when to use "yes" and when it is okay to use "no"...and that is tough sometimes. Simple things are easy. "Can I borrow a cup of sugar?" "Yes!" "Can you help me change this tire?" "Yes!" But what about these questions:
"Can you watch my dog for three weeks?"
"Can I borrow some money?"
"Can I store 50% of my stuff at your house for the next six months?"
You may want to say "yes, no problem, I will rearrange my life to fit your needs." But for your own sanity, sometimes you have to say "no". While the actual word is not difficult to say, the guilty feelings that follow are sometimes overwhelming. Each situation has to be handled individually and with both your needs and their needs in mind. If, after 24-hours of pondering, you determine that the impact to your life will not have any negative long-term effects, then go ahead and say "yes". But if you find that even the tiniest amount of resentment may rise up, or you may have to adjust your schedule to something you are not comfortable with, then say "no". Allow yourself to put your needs first and even if you do feel guilty, it will pass in time.