What helps...Stay calm, step back, breathe and reply to them 'later' rather than a knee jerk reaction.
What to avoid...Try not to lose your temper, much easier said than done. Don't keep trying to contact them. Maybe one text a night is OK, I tried this at one time and it worked. Other than that leave a gap of a few weeks before trying again, that's if they haven't cut you out of all forms of contact.
What works...I no longer know because as I struggled with the silences and pulling away and not contacting him, i eventually snapped and I now haven't heard anything for 3 weeks and know I never will again.
As said above by Al-Lurker, try to gently encourage a person to get help. I felt doing this by finding professional and well known services who would do email counselling might be worth a try as the person I knew couldn't talk to anyone face to face about one issue so I felt this might help. In the end he couldn't do it, but it was worth a shot.
I wish everyone the very best of luck on a very tough road.