How do you respond to someone that hates themselves?

Have an ex that constantly self deprecates. The “I hate myself”, “I’m a worthless piece of crap”, “I don’t deserve your apology and love.”, etc. Myself and many others have already called him out on his self sabotage and him being aware that he self deprecates. He’s been drinking a lot more which also makes me concerned but at least he still goes to the gym. I want to at least be there to listen but I’m not sure on what to say. I just want him to do better and I can see that he’s stuck. What even can I say as an active listener to someone that’s venting?
How do you respond to someone that hates themselves?
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