That’s traumatizing. Not sure if there’s anything you can do. To him, you said you saw your future with him but from your actions you didn’t. I can’t imagine finding out your SO tried to end their own life while you weren’t there to stop them.

He’s breaking up with you because you’re unstable and he most likely can’t take someone messing around with his heart like that. He’s protecting himself by distancing from you.

Get the help you need and give him time. You could try to rekindle the relationship in a few months or years but I don’t know if it’s possible.