why?

Why does it seem that when everything is finally going right, a bomb (or in my case a few) gets dropped in your lap? Why is it that the people you are closest to are the ones who are soonest to push you away when they start to make the wrong decisions? and WHY WHY WHY can't I stop caring? I know it's not helping me to continue to try to reason with her, and I know that no matter what I say it won't make a difference, but I don't wanna see her get hurt, and I just can't stop myself. I am praying for her, but I also wish she would just realize that I'm not out to get her, nor am I jealous of her happiness. Why can't I make the difference in people's lives that I thought I could? and why is this affecting me so much?