Hey lillies, welcome to PC sorry to hear your in such a bad place.
A couple of questions, have you been to your dr, diagnosed and prescribed?
Have you caught out a T.
Suffering from depression myself, when my partner of the time had a breakdown I managed to keep it together but it took it's toll.
Altering the way I looked at him. I didn't feel like his lover anymore I re but like a carer, his parent almost.
I don't know if it ever went back to the way it was.

It's too much to care for another when your own MH needs aren't being met.
As hard as it is to hear, you need to take care of yourself, your ex has realised no-one can fix him but him.
Now you need to do the same.
I really hope your able to take those first steps,and rather than think "how can I do this now he is gone."
You need to think, "I must do this, because he has gone, "

He is not there for you to focus on anymore, you need tone brave a focus on yourself.
Good luck, and all the best.