hopeless

Where do I draw the line? When is "the addiction" just an excuse? When does she finally step up and take responsibility for her actions? Ever?
I am just so tired of it all. I thought I was tired of it months ago, and yet, on we go. I want nothing more for her than a reasonably fulfilling and rewarding life. That, it seems, is too much to ask. At least for right now.
What to do? I have had to keep her at arm's length, or further. It just hurts too much to let her back in, let her get close, involved and then get my heart trampled on again. I understand it's not personal. That doesn't mean it is not painful. I get too invested when she is too near. I find myself believing, hoping, and then crushed all over again.
If anyone reading this is struggling with a loved one who is an addict, I empathize with you. It is a heartbreak you can't understand unless you have felt it. If you have a success story, please share it. I have absolutely given up hope. If you have any, I welcome it.