Unfortunately people are rarely understanding and see suicide as an act of weakness and cowardice. It kills me to say that.
However, sometimes there are some variations. Some say they accept the choice of the CTB person. But in reality, they think that we say that for fun, to attract attention and that we just have a little depression. Afterwards, if your partner is really understanding, caring, emphatic and doesn't talk like that, I guess you can talk to them about it. I told someone very close about my plans and I think she's in denial. She doesn't understand that it's almost over, it's as if I hadn't said anything. This person keeps talking to me about the future and asking me why I have to get rid of and give away all my stuff.
There is always the risk that she will call the police or the psychiatrists. It is a risk that must be considered because we do not know how people can react. I did not imagine that the person in question was going to be in denial, I really thought that she was going to understand and enjoy our last moments.
And there is always the solution of breaking up before the CTB and not telling anyone.
I sincerely hope that you will be better, and that your partner is an understanding person. Life is already very difficult, and it is often heartbreaking when these kinds of problems interfere with our loved ones. I wish you the best.