How to ask my narcissistic boyfriend with depression to be just friends?

I’ve been in this relationship with him for 3yrs but I’d rather be friends and I’ve told nicely before and he just says he’ll do better and then we can work on it together but the truth is I just don’t love him in that way and would rather be friends but everytime I try to break up with him he threatens to kill himself and as attempted multiple times to keep me with him what do I do?
How to ask my narcissistic boyfriend with depression to be just friends?
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