I'm sorry that it took this situation, and hurt feelings, to bring you to the realisation that there are friends, and then there are people who will only be with us when it suits them, and gives them something. Fairweather friends is the phrase my mother used to use.
I have found that when you have real troubles hit in your life, extended illness (or permanent disability in my case) job loss, family emergencies, a death of someone close to you, you find out really quickly who your real friends are. Dr. Phil says that "real friends are walking in the door when everyone else is going out." I have had to learn that while it is necessary to have some aquaintainces in life that are nice to be around, that I cannot expect too much from these shallow relationships.
You sound so much like my mom in that everywhere she goes, she HAS to talk to people, she has had a habit of 'collecting' people with serious problems (addicts, prostitutes, etc) her usual MO is to try to "study" with them. But this habit made growing up in my household a nightmare. More than once I had to fend off people that followed mom home, who she let in with open arms. Only now, as a parent, do I realize how dangerous her inability to say no and set healthy boundaries was for us as her children.
You have to get over the inability to say no, and set those boundaries. Otherwise you're right, you will be empty and have nothing to give to yourself, or anyone else. Nurture yourself, I recommend reading Martha Beck's column in Oprah magazine for starters. Go to the library and look at past issues of the magazine, I believe that her perspective could help you a lot. I know it's helped me.
Only by getting rid of the psychic vampires from your life (the people who suck you dry and leave you exhausted) can you be a good friend to yourself, and to the wonderful nine people who showed up to celebrate with you. As far as your siblings...you've learned a hard lesson that ihad to learn myself a couple years back that my siblings CANNOT be counted upon in happy times, or sad ones. They just don't have anything to give, or share with me. They can only perpetually take. And they can only take what I let them, which is a lot less than it used to be.
Be good to yourself, and remember to send a little card to everyone who came to your party, because friends like that are worth cherishing, and holding on to.