I'm stuck

Here goes, my husband of 20 yrs has been diagnosed with clinical depression and has tried to commit suacide several times. He has always had ups and downs but after the death of his mother 4years ago he has been a different person. I have sought him professional help which only made things worse. I am so fed up of this whole situation i am concidering leaving him but i cant bring myself to it. I would be letting him down and my children. I have tried everything i can to get him on the path to recovery but its like he dosnt want to get better. What do i do? Do i stay with him in a miserable life or do i leave with the worry that he would end his life if i did leave. I couldnt live with the guilt if he did. Any advice or opinions would be greatly welcome.