Leave him. Tell him you need to figure yourself out before you can be in a relationship, and that being in a relationship is too much for you to handle right now. Which is true. And then go get help.

He'll probably fall for another narcissist anyway, so I wouldn't worry too much about it.

Or, you could let him decide what he's willing to put up with in order to feel happy and fulfilled. He's an adult with his own reasons and desires, after all. I'd still take a break from the relationship so that you can sort yourself out, but maybe he'd be willing to wait.