How to I get my therapist to understand the intensity of my suicidal thoughts without them bent reassured that things aren’t that bad because I’m talking about it?

I’ve always been under the impression that professionals believe that, if someone is being honest about their suicidal thoughts, then it’s reassuring as they mustn’t surely want to go through with it or they wouldn’t tell someone. I’m genuinely and utterly completely suicidal (although I have no active plans to kill myself within the next 24hours). I feel that if I be honest with my therapist about my thoughts, they’re going to think I mustn’t really want to do it or I wouldn’t be speaking about it. Is this the case?

I’m also acutely aware that, if I tell my therapist I have a plan / intent, they would have to breach confidentiality so I obviously wouldn’t tell them that.