Most people drink and use drugs to try and deal with some underlying problem. The feelings of worthlessness are probably not new, they've probably been around for a long time.
When a person gets really upset about something, it's usually because that circumstance shed light on some underlying belief that is painful to them. Drinking and drugging can keep those beliefs in the dark, when a person stops using, those painful ideas and beliefs are still there. A lot of people aren't even aware of this, they just live life as a series of automatic reactions.
Trouble at work > It's my fault > I'm worthless > Anger, depression...
Can you think of anything that makes you really upset? Can you then trace that back to some underlying insecurity or belief that is painful to you? How about the way you're feeling right now? Are you upset at him? Are you upset or frustrated with yourself for not knowing how to help him? If you can start this process for yourself, then you can also start to see it in other people as well, in the way they react, and you can see things from their perspective more easily.
What would you say to a person who had an underlying fear of being inadequate or worthless? Would it help them to point out that this belief might be conditioned from a long time ago, and isn't true?
Just remember that you can't fix or change a person, you can be supportive, but trying to fix someone is exhausting. Good luck.