Yes, that's a cliché, but that's only because it's so doggoned true. Another way to put it that I think is applicable to this situation: you can throw a drowning person a life preserver, but you can't convince them to reach out and grab it.
I understand the urge to rescue all too well, but some people just. Will. Not. Allow. Themselves. To. Be. Rescued. No matter how desperately you want to rescue someone, it may simply not be in your power.
If this guy does have borderline personality disorder (and it sure sounds likely), I'm afraid the chances of your being able to convince him to get help are vanishingly small. I really wish I had some brilliant advice on how to get this guy to understand what he needs to do, but I just don't. I am so sorry. 
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