Kissingfrogs, your experience is so similar to mine in may respects that it is uncanny. I do recall very clearly the time when everything came to a head, whereas the weeks leading up to then are a blur, as I was getting very little sleep.
The night exH stuck the knife in the pillow he went out for a long time, while I was settling DD1 (who had found the knife there) and DS, who had also been awoken. He told me when he came back home that he had been standing by the electrified rail line intending to walk onto the third rail and do away with himself. Obviously he had come home; while he was telling me about his walk, I remember noticing (and remarking inwardly to myself) that his eyes were completely calm and watching me closely all the time, though he was flinging his arms around and his voice was very dramatic.
I felt there was something a bit unbelievable about the situation, something he wanted me to believe that wasn't true. I felt extremely alienated by his talk of suicide, and there were times I sincerely wished he would just get on with it. Not proud of that, but it was manipulation pure and simple, and as Kissingfrogs said, anger cuts right through all of that. I persuaded him to go to bed and at least lie down and stay in bed for the night and to go to the nearest full service psych ward in the morning. He went under his own steam. The doctor who admitted him called me to get details about his behaviour.
His parents and sister arrived the same day and basically camped out in the hospital. ExMIL told me later there was nothing wrong with her son but a bad marriage, and that this was what the psychiatrist had told her. Because the parents and sister were there constantly exH didn't participate in the workshops and craft sessions that the patients were supposed to take part in (and the staff didn't push them out sadly, although I know the exILs exFIL was a doctor and it would have been very difficult to shift them).
So exH was encouraged by his mother to believe he was basically in a place where he didn't belong and where the rules didn't apply to him (a major misapprehension he has suffered from all his life), and probably persuaded him that all his troubles boiled down to me. (He accused me many times afterwards of driving him to the brink of suicide, and I felt more and more alienated every time). He wouldn't even take sleeping pills in the hospital despite his severe insomnia. His father, a doctor, was just about the most ignorant man I have ever come across when it came to MH issues, and I think he probably had something to do with the sleeping pill refusal.
He came back home after his hospitalisation, which lasted less than a week. I didn't want him to come straight home and we all agreed that he would go to exILs hotel for the night and then come home the next night. This was after exFIL accused me of trying to throw exH out of his own home.
The relationship hobbled along for another few years, but it was obvious to me from the continued accusations and blaming that it was really over. We have a joint parenting agreement, and he has visitation with the DCs every second weekend, plus bits of holiday time. He has taken me to court on contempt motions several times, and has threatened me with contempt motions several more times, whenever he has felt that I have proved his basic hypothesis about me right -- that I am determined to steal his children from him, and deprive me of his rightful time with them. He asks for punishment and public humiliation of me in documents he submits to the court. So far, the judge has refused to entertain any of this irrational BS.