I lived with my partner for the last two years, we had split twice before living together due to his seeing other women. I believed he'd changed. We don't believe in marriage but he bought me an eternity ring on a romantic holiday without our children. About a month later I found emails of photos of another woman ( not classy photos) who he always said was an old dfriend. He apologised begged for forgiveness, stupid incident when vhatting and things went too far. I gave him the benefit of the doubt bit trust was difficult then 4 weeks ago I found more emails but about what they would do to each other when thy next met ( a different ex girlfriend this time), he admitted having an affair on and off for a year. I left, enough was enough. He begged and professed undying love, guilt sorrow, do anything etc and this went on for 2 weeks. I never responded in Amman way as I knew he could turn nasty and vindictive if he did not get his own way but stayed form.
Last week I got an email calling me a sanctimonious and saying that I would feel the guilt and that he wants to be one of my demons because if he can't have them no one can. I sent my friends husband who found him hanging. We were rushed to a and e and he was put in to an induced coma. I stayed there bit was told not to actually see him as if he died he had left me with a bad enough memory without the visual and if he lived and I was there it would give him false hope ( that was the gentle description) or show him manipulation works. He came round and asked for me and told everyone it's me who is selfish for it giving us a chance I am cold etc bit then sent me a text telling me his actions proved his words were not shallow. Now I am feeling permanently guilty and worried he will do it again but can't see him and feel cruel.mites all so confusing. My son phoned me in tears about something else last night and I woke convinced he may have tried to kill himself, totally irrational.
I don't know what to do, I'm not bereaved as he is still here bit I'm scared, guilty and drowning

I'd call the authorities... specifically the Police...

Saying that if he can't have you no one can.. is more than an idle threat.. its one you should take seriously.