hey love hurts!!
From the things you told in your letter, It's hard to really have a solide and underbuild opinion of
your relationship with this man and his caracter ( that is essentiel).
But if I was to go with my first gut reaction I would say ( how ever hard this may be), you have to let go of this person because if he reallyl loved (and he obviously doesn't love him self ) you, he would not, make you go true the agony of fighting over and over again.
If he wanted to be with you so bad( for what ever reason, love, not beeing able to be alone etc etc) he would have been on your door step a long time ago( what ever the consequences).
Or you have to make him change his ways by looking for help to overcome this yalousie thing. Before you ever get married, because this is going to go from bad to worse.
And being on the phone with someone threatning to kill your self with a gun sounds kind a cowerdless to me.
Remember people that threaten to kill themself often don't have the gut's to do so!
I'm sorry if this is probably not what you wanted to hear but I hope you get some help out of the advice you get from people.
Don't mind the my writting mistakes plz, not english, from holland.