VS Crisis Management

I can't wirte details at this moment, but I must think seriously about Crisis Managemnet now.
One of my friends seems to have been in a trouble with a stoker.
The friend (I call F) might not accept it fully because the stoker (I call S) was a friend, so F doesn't want to call S a stoker.
However, from my view point, S is now becoming a stoker.

Perhaps, S liked and still likes F. But F doesn't like S so much. S's heart was broken.
After that, there had been no connection between F and S for a few years, but recently F started to see S again.
I heard from F that now S think somebody is disturbing the relationship of F and S. And, S concludes the somebody is me! Even though I have not seen S for five years more. Thank you for remenbering me.

Last week, S showed up in front of me suddenly. I was on the way to a restaurant with F, so we went there with S.
I didn't know the story written above then, so I tried to communicate with S gently in the restaurant. I talked about my life of last five years and asked for S's current life. At first I didn't find anything strange with S, but soon S's attitude changed to become offensive toward me.

S started to talk about S's handy phone. I couldn't understand why S talked it but listened carefully.
S says, "You know why I am here now? (I said, "I'm not sure.") Ok. Somebody invades my phone, checking my email, my text etc. That's why I can't send any message to my friends. I can't communicate with anybody. You know why I'm here now. It's a stoking to invade other's handy phone! You know? My phone is not old and not broken. It's new. But, there are something strange in it. Because somebody is invading it! It's a stoking! You must know why I am here now."
S is looking at me with anger. Gradually, I realised, insted of S's phone, S's mentality is broken now.
S refered to somebody's stoking S, but the hidden message is that S itself is a stoker.

Our conversation was finished and S left the restaurant without saying goodbye.
I couldn't eat more. It was no taste. It was my first experience that we lose the sense of taste when we were in a very bad mood.
On the same day, I had a meeting with my friends. What should we do?
Fortunetely this crisis is on the very early stage. S is now strange but can be treated to be normal. We will try to make S's family take S a hospital.
S was offensive but not viorent. We don't worry about physical crisis at this moment, but if we would recognize it, we will take S the police soon.

I couldn't write more because of my friends' privacy. But the above must be enough for documentation.