I am sorry @Marfar77 that you are having to navigate the very rocky path of dealing with an unmedicated spouse. I want to try to answer your questions, even though it was my daughter I was caring for. Getting a loved one onto the proper medicine is very hard usually, no matter the relationship.
To your first question: No it is not terrible for you to want him to tell you he plans on hurting himself so you could call the police and hopefully force meds. I wished that for years while I dealt with psychosis. I did call the police several times myself when my daughter made mention of harm to self or others. It IS a path that works for some to use the police.
To your sentence in caps: Yes oftentimes the loved one needs to be medicated to understand they needed to be medicated. But sometimes, even when medicated, they don’t understand they are ill and need medicine. My daughter takes her meds because she can hold a job when on meds. Not because she is ill…
“If they’re held against their will, do they keep them until they’re stable on meds?”: It depends on the doctor, the hospital, who is paying, and how fast the meds make improvement. There is no guarantee that a person is “stable” when released, and sometimes they are released still very unstable and sometimes with no where to go.
“When the police come, can he get out of it by acting normal and saying I’m lying?” Yes, the police have to make an evaluation on how the person is acting when the police come. Your loved one could “turn it off” in front of the police.
There were over 40 times that the police were at my home with 3 forced hospitalizations from my home. There were also two arrests with forced hospitalizations from the jail. It was a terrible path, but my own personal result for my daughter is that she has been stable on meds that were at first forced on her in Dec 2018 after her illness began in Mar 2016.
Your path in helping a spouse is different for sure, but perhaps calling the police one night when he says he should be dead could work… especially if he says that he should be dead to the police when they are there. My daughter never really got mad at me for the police coming to our home or her forced hospitalizations. But only you will know in your heart what actions are required for your situation. I hope things get better for you.