The O.P. asked whether one could be forcibly hospitalized for discussing suicidal ideas with a therapist. The short answer to that question is "no."

It would be unfortunate for Bats to feel afraid to honestly discuss thoughts and feelings with a therapist based on an unrealistic fear. Bats has an unrealistic fear. I would encourage Bats to be open with the therapist.

I don't know how suicidal or how rational Bats is. A therapist who knows Bats is in a much better position than me to evaluate that. The therapist might very well encourage Bats to go to a hospital. It might be the best thing to do. Or not. Therapists don't automatically tell everyone who discloses suicidal ideation to go to a hospital immediately.

The question was about involuntary hospitalization. I was explaining how involuntary hospitalization comes about.