My understanding is that therapists have an ethical duty to provide you with a disclosure statement before they start treating you. The disclosure statement would include the circumstances under which the therapist can and would break confidentiality. For example, if they genuinely believe that you are a threat to yourself or someone else.

However, the reality is that a lot of therapists, particularly older ones, don't follow this ethical guideline. I've never received a disclosure statement from any therapist, except Talkspace.