“While I understand it’s best for me, I really want to help him and not make him feel rejected. How can I help him? How can I stop him from hurting other potential partners, whom he will inevitably hurt as well?”
Answer by Joseph George:
This is what you should accept first: You cannot help your ex. Nor, despite what you may wish, are you able to help him with his future relationships.
I have no doubt you care deeply, deeply for this man. You have made what appears to be the right decision to end a very toxic relationship. Yet you appear to be clinging on to him for no other reason other than to ‘help him’.
You should consider if your altruistic feelings are in fact altruistic in nature or a subconsciously triggered mechanism for ‘safely’ engaging with your ex, possibly because you still have feelings for him.
You have mentioned that he is highly intelligent. He is probably aware of his issue more than you suspect. Raising it, in any manner as non-confrontational as you wish, will not end well, because you will be in his view, merely ‘exposing’ him, and being unnecessarily cruel (in his eyes). You have already drawn his attention by breaking off the relationship.
Now it is up to him. The best you can do is to disengage.