Beachside,
I don't think there is a protocol, other than what your heart can take.
I've personally changed my social itinerary so that I didn't have to take a front-row seat to a friend's relapse/meltdown. I knew where I'd run into her, and I chose to go somewhere where I was sure I wouldn't.
That's for my own sanity. I know what a punch in the gut it would be to see her that way, and I'm not into drama any more (I used to be!)
Hugs to you and prayers for him
GL