Good job on going to the movies with your brothers. That's a step towards detaching. And its good that it pisses her off. Let it. Keep working on your detaching; you're not there yet. Dropping the rope and detaching isn't about giving up. Its about not letting them control your emotional state by every little thing they say or do. You're still in that place so keep working on it. I know how you feel. I know how sick the thought of losing your W makes you. But its not until you truly let them go and are willing to walk away that you can begin to save your M.
Some of the best advice had seen in a bit. Being sick at the thought of losing her is understandable and something that all us have - and still do to some point - expercienced. This may sound very harsh, but she's already lost. I believe it was Sandi who said it best - (to paraphrase) there is no going back to what it was, if there is a rebuilding then it will be completely new. Kind of like dating all over again, I guess. But what was had is gone and was before the BD.
Take care of yourself first. It's kind of like living as if she weren't part of your life in any form and never was, if that makes sense. This is all about you now. I know it's hard and, hell, I can't fully follow my own stuff at times. This [censored], man.
There are moments in this life when you are so confident in the rightness of your actions, that not even for a second do you consider the option that you might be wrong.