Can bitterness ruin you?

Recently I have been feeling very bitter. The friends I use to hang out with never call me back. I will note that we live in seperate cities but does it really hurt to call a person back? In addition a job I was really looking forward to starting fell through. It was one that could help get my life and career on to a running start. I realize that this won't matter in a few years and there are others far worse then me. However, these events have lately really bothered me. Help what should I do?