That brings memories of my late husband who had recurrent major depression. It was painful to both of us!
Suggest: get him professional help and come to an agreement with that person that you are a partner on your spouse’s team. Know when to notify the pro that things are not going well. It was a great relief to me just to leave a brief message on his answering machine such as, “He’s talking about suicide again and says this time he knows how and when he will do it.” Hearing that more than a few times from my husband was a terribly heavy burden. It was a relief to be able to pass the responsibility of that message onto the pro.

Get professional help for yourself because you will need it. Please be assured that someone else’s depression is not your fault. Know when to stay away and leave spouse alone. In short: save yourself. Finding an understanding friend who is a good confident can be helpful, though no one can truly know what you are going through. It can be a heavy load, and it is up to you to find ways to uplift yourself via escaping for the day, seeking humor wherever you can find it, and pampering yourself where that is possible.

After a very long life my husband died a normal death. Subsequently the pro said, “No one else could have kept him living that long.” We both knew it was true.