My best friend have recently been spending a lot of time with some people from her work. 
That stinks.  I always feel left out when that happens to me.  Even more so when I know the people from my best friend's work so when I can't be involved, its hard.  How do you feel about it?
I am not happy  that it seems she doesn't have much time to spend with me anymore.
I'm sorry.  Make sure to reach out to her and tell her how you feel.  If she's a good friend, she'll understand and make an effort to make time for you but don't let it make you bitter.