The way you've described his texts, he has said he would rather either end the marriage or die. I would personally take him at his word and say OK, pack your stuff and fuck off then.
I'm afraid after years of doing the co-dependent jolly-him-along please-don't-leave-me dance thing with a couple of previous partners, I've got terribly bored of that. Any partner now who tries the "I'll leave you unless X" tactic gets handed his belongings in a small bag and wished good luck for the journey onward!
I have come to realise that a relationship shouldn't be about me sitting there trying to puzzle out "Oh he said X but I think he meant Y, or possibly Z." I now just act on the basis that if he said X, he meant X, and if he was lying then its tough shit on him.
At one point... not my finest moment I admit... I was sat in relationship counselling with an X. He was moaning on because he had told me, repeatedly, that he didn't want to celebrate his birthday that year. I had asked him if he was sure several times, and he kept saying yes. So I didn't buy him a card or present, or take DS to buy him one. He then said in counselling "You should have known I really meant yes I did!" I said "So you were deliberately lying... why?" He couldn't answer that sensibly but kept repeating "You should have known I was lying and gone against my wishes, which were really the opposite of what I said they were!"
So for about the next fortnight, every time he asked me for something, e.g. "pass the salt", I would give him something else. And then say "Oh sorry, I assumed you were lying." God it was childish and petty, but it FELT SO GOOD 