I am sorry for your pain. Sounds like your ex reached out to you as a reliable source.
How to help him????
All you can do is recommend that he seek out a professional as soon as possible. Remember, this is his recovery (or lack there of) and there isn't a single way you can do it for him. Sorry, but that's a fact.
All you can do is be a friend and be honest with him. He honestly needs professional assistance. What he is experiencing could be Depression and that is something that a well meaning, caring person (like yourself) is unable to handle alone. You can be there to talk to him, to laugh with him, to listen to him, but he needs a professional to get through this kind of pain.
Please urge him to contact a therapist or even his family doctor is a start. I don't know if you have such a thing in your area, but a crisis hot-line can even be a source of help.
We can help you with our own experiences but if you truly want to see him be successful in his recovery, strongly suggest he gets a therapist. It is his choice to do so or not.
You are in my prayers, please know that you are not alone and we are here to talk.
There are also some great postings on Therapy, Depression, etc. Take some time to read these. They can also be a great source of information as well as comfort.
"Insanity is doing the same thing over and over, and expecting different results."
I cannot take your steps, but I can walk beside you, if you'll let me.