"when he threatens to kill himself/never see the kids"
yes had this experience - how serious is he?
one time "i am going off to xxx country and the dc will never see me" - when challenged became "i just said i was going on holiday, dont know what you talking about..."
let us say he actually does kill himself - would you be repsonsible for that? no. his responsibility. his decision.
yes you would have to deal with the fallout and support the dc - but that would be doable and you could get relevant support.
as was said - the only response to "i am going to kill myself" is dial 999 and get police/ambulance to go see him ... if like my ex the police will call you back within an hour or so and say they have been to see him and he is absolutely fine and wonders what the fuss is all about...
or - if really serious - then they will take the necessary measures eg psych ward.
either way - responsibility becomes someone elses...
contact - depends how old dc are - if young then stick to contact centre, keep record of suicide threats etc to take to solicitor.
get him to make them by text/email if possible...