Most people have it wrong. The method for fighting for someone who has pushed you out of their life isn’t by begging for your life, describing every thousandth reason why you should be together, crying, blackmailing therefore reconfirming the reasons why they went away in the first place.
You fight by giving them space, enjoying the things that make you happy and your life therefore reminding them of the reasons they fell in love with you in the first place. Here you’re fighting for your own life, to get it back. Not theirs. You can’t make someone else happy when you’re not happy with yourself.
If despite all this, their interest is never regained, at least you should be able to live with that by then. Be strong. Make your own life come first. Then walk away.