How do you handle it?

First off, I want to thank everyone who has been so supportive of me through this break up.  I've come to the realization that I can't fix the fact that my ex is bipolar and that it is not my concern if he is not diligent about getting it treated.  With that said, as hard as it is, I think i'm going to have to walk away from this...even though I know he'll be back as soon as he stabilizes, as he always is.

Even though I have chosen to put myself first (for the first time in a long time), it is still breaking my heart to watch him go through this.  For instance, today he posted online that he's booking a trip to Europe.  One of the last conversations we had was in reference to how he was going to have to save every penny he was making to be able to afford a new car in a few months because his is on it's way out.  Now he's going to Europe.  Part of me wants to call him and try to talk some sense into him, but then i'm just being pulled right back into the destructive cycle he has me in.

What I want to know, is how do people deal with watching this go on?  I know just about everyone here is doing everything possible to be treated properly and are fully aware of their condition, but perhaps before you were diagnosed or something.  I just find it so hard to walk away from him when I know he's being so distructive with himself.  It's so hard to watch someone you love hurt themselves and knowing there's nothing you can do to stop it.

Thanks for any advice you have!!