I have not told my significant other about my plans either. It's a dilemma. I know that she loves me more than anything. I hate that my CTB will hurt her. It's one of the things that is still keeping me here for the time being. I am sure that she would not approve of my decision either and if she knew about my plans she would have done the same as your significant other did to you.
I have accepted that no one in my surrounding understands suicide and why some people goes through with it. I am not sure if someone who haven't been through such a state of mind is capable to comprehend the nature of the situation. A non-suicidal person is trained by modern society to "help" people with depression and suicidal thoughts by "rescuing" us by preventing suicide. So in a way it's an act of out of love.
And I can't say that I am against it in a way, because if a person can be persuaded to keep on living my opinion is that he/she wasn't ready to go through with it anyway. And I think that lots of suicidal people want to be saved to feel a sense of love. I know I felt like that 10 years ago.
However some suicidal persons cross a line where there is no turning back. I know that I spoke more openly about suicide and depression when I were younger with my family and friends, they all knew about it and at that time I wanted to be rescued. I wanted someone to care about me.
And now when I am more serious with going through with it. I am not talking as openly about it because I do not want anyone to try to persuade me to keep living since it's already to late for me. I do not want anyone to feel like "they tried to save me but failed".
Since you apparently did not tell your SO I assume you were serious with going through with it when the time was right. One of the reasons why I do not speak about it openly is also If I decide not to go through with it I do not wanna damage my relationship by her worrying about my well-being. I wanna do it in my pace and without people knowing and expecting stuff to happen.
Yeah apparently it's the modern society that decides when and when not to own your own body. It's hypocrisy...
I understand your frustration, send a pm if you wanna talk