what can you do?

What can you do when you want something that you know is wrong for you but you go on wanting it anyway? It's like you know all the flaws up front, you know that this probably isn't right for you, you know that you don't act like yourself when you're around this thing you want. Why do you continuing wanting it? Why do you want those things that aren't good for you? You've been there before, been hurt before because you tried to make it work with something that was bad for you... and here you are again. A different kind of bad for you but none the less, it's not good. So, what do I do????