I was once in a situation similar to yours in that I had a dear friend with serious physical and mental health issues. She had severe asthma, depression, and I think she was bi polar to boot. I did the best I could to help her and in the end it impacted my own health and I was having trouble taking care of my obligations to my own family. I was fortunate enough to have a wise friend who was also a social worker. I will tell you what she told me and you can take it for what it is worth. First of all, she said you cannot save another person. They have to do this themselves. You can listen to and support them, but beyond that, the services of a mental health professional are needed. You do not have the skills or the capability of doing this yourself. Secondly, she told me that if a person goes off the deep end and does something drastic, remember that it was their decision. The chances that you could have prevented it are slim and none. I am just putting this out for what it is worth. I don't know if it will help you but it helped me.
Just a comment. I have a cousin who lives out of state and who is dealing with depression and anxiety. She sees a therapist and that helps, but the doctor just put her on some medication and she says it has helped her a LOT. That is something to think about too.