I sure feel for your friend. I've been there.
My suggestions are to not at all attack his belief system at this time. Rather, be a true friend and confidant. Check in on him. Invite him for a walk. Get some iced tea or other refreshing drink - not alcohol.
If the conversation goes to his thoughts of harming himself again, ask if he is flirting with thoughts of suicide. (I have asked this question of a couple people. You have to watch their face and eyes when you ask that question because you will see split second expressions on their face. I've been asked this question - and answered 'yes' truthfully.)
If the answer is yes, the next question can be: 'Do you have a plan?' Most people who are seriously considering suicide have a plan in mind. They may tell you 'yes' but will be reluctant to tell you what it is. I have never told anyone what my plan was. I had two separate ones that I was musing over.
The important thing for you to do is to remain non-judgemental and non-emotional. You can verbalize the words 'i'm concerned about you and I care about you.' Simple but truthful statements can help ground him and let him know that you are someone he can trust to unload his thoughts to.
Making specific plans to meet up again (ie: Wednesday after work to play tennis) and then call a day or two beforehand just to confirm. (1-2 minute call) Listen to voice over the phone. You can start to tell where the person is emotionally. Commit to a date and time and keep it light-hearted and fun.
This gives your friend something pleasant to look forward to.
To get him to agree to take time for fun, maybe share with him something that a pioneer told me. I was working fulltime and also pioneering along with other responsibilites and was starting to get very rundown, stressed and depressed. She told me that you cannot give what you don't have. You have to take care of yourself first before you can take care of others. Sometimes it's important to step back for a little bit in order to properly re-charge and nurture yourself.
I didn't follow her advise then but I sure remembered it when I spun out of control and had my breakdown. It was not a pretty sight. But lesson learned - unfortunately learned the hard way.
Oh! I really liked what AA said: They tell everyone to do more. Even if he was putting in 100 hours a month, we all know -he does, too - they would still be encouraging to just a little more. It's never 'enough'. So it's up to each of us responsible adults to realize that sometimes we have to slow down a little before we seriously hurt ourselves mentally, emotionally, spiritually (to our core), or physically.
Be an understanding and truthful friend to this person. Sounds like he needs (and will soon realize he needs) a real friend to whom he can unload his honest feelings.
Warmest regards to both of you.
-Denise.