Cold hearted

Some people know just how to push your buttons. Right now there is so much going, and my life is consumed with summer school at the moment, and that is enough stress and work as it is. I have this person who used to be my best friend, but just because I didn't hang out with her when everything was going on 3 months ago, she decided not to be my friend any more (very mature). Why can she just leave it alone then? Why does she have to text me, get me all riled up and annoyed. I never know that some people could be just so cold and couldn't care less that you are going through a hard time, they just want to make it harder. It just AMAZES me how much some people just don't have a heart...but it is probably for the better to find out who my true friends are now rather then later