Where does selfish cross the line?

As a parent, you are generally expected to lose all of your "selfish" tendencies for your child - right? But what about the other areas of your life?!? When is OK to be selfish?
I consider myself VERY selfless when it comes to my son... for those of you who know him - you KNOW the poor child doesn't go without much of anything. As hard as life gets, come hell or high water, I make sure he is taken care of first. So that makes me a good mommy - right? A good selfless, put my child first mommy :)
NOW - let's talk about the rest of my life.
I spent alot of time with a very close friend this weekend and when asked, she described me as NOT being selfish. I had to argue that point.
Don't get me wrong - I don't go through life walking over people and not caring who I hurt along the way, BUT I have found, that as the years pass and I learn more and more about myself - I have become what I lovingly refer to as a bit selfish!
Let me explain...
I'm a giver by nature.... it's just who I am. I go through the day pushing myself to the limits to do just about anything and everything that I can do in order to make others lives easier or better in some way. I make sacrifices.
BUT - at the same time, there are certain times and things that I'm unwilling to compromise or give up. That's not to say that these things won't change some day and that in the right circumstances they couldn't be compromised.... but right now - as a single 33 year old mother with entirely TOO much responsibilities to get through most days.......I'm gonna hold on to my single girl selfish vices and if people judge me - they judge me!

So - my question for the night is: when is selfish crossing the line?
Is there a fine line you can walk in order to make others happy - while at the same time making yourself happy? (this is how I maintain my sanity!) ha ha
And if you walk that line and don't "cross over" - then is my friend right and I'm NOT selfish? Sometimes I worry about those qualities in myself...
AND - if you hang on to those "selfish" traits in your life - should that label you somehow as a bad person?
Or to come full circle.....does being a bit selfish make you not "datable?" I'm just curious about that because the older I get and the longer I'm alone - I think I tend to get more and more "selfish"
Hey - someone's gotta look out for me - right?!?!!