Make sure you have a safety plan in place
https://bpdfamily.com/pdfs/safety-first-dv-1.pdf. When having this conversation with him, you will be at the highest risk for IPV and/or abuse when you do this.
Recommend having this in a public space (park, indoor shopping mall, preferably with video cameras) where there are witnesses nearby if it goes south and he becomes dysregulated - make sure you record the conversation that way if it goes south you will have irrefutable documentation on it. Don't do this by yourself if you are able, have a friend or someone you trust physically by your side, this will also reduce the chance for it to go south.
If you haven't already done so, be sure to read "
Splitting: Protecting Yourself While Divorcing Someone with Borderline Or Narcissistic Personality Disorder" by Bill Eddy and Randi Kreger and understand everything in it. Google has the first few pages, which includes the 'quick start guide' at
https://www.google.com/books/edition/Splitting/WxQxEAAAQBAJ?hl=en&gbpv=1&pg=PT8&printsec=frontcoverGood luck, and take care.