People threaten suicide every day. We can look at the statistics and reports and use those to make our decisions, yes. But in the end you know what this person is doing-using his trump card. My brother who was addicted to EVERYTHING used to threaten suicide with everyone for years. I would worry myself sick and run home frantic from work at lunch every day to check and make sure he was OK, scared to death he'd blown his brains out in my house. We all finally got to the point where we would just say, "Go ahead." He never did.
You got away from your ex, got some peace and serenity, and then, as soon as you started accepting his texts, the madness, drama, stress, fear (and all the "WHAT do I DO?'s) are all returning to you. HE is reponsible for his own emotions and feelings and he is ABLE to do what is necessary for his own life. If I were suicidal I'd call a hotline or go to the emergency room, or call my doctor. If you call the police, what will result? I had the police help me with my brother and they made it WORSE. He nearly died at their hands when they were supposed to HELP.
When you try to play God, when you decide that you must act on another person's behalf, you then become responsible for the outcomes. If he dies because HE decides to, that is not on you. If he dies or is otherwise harmed because of your intervening, how will you handle that?
Here's what my brother said to me after the whole police episode: MIND YOUR OWN BUSINESS.