I would recommend having a plan in place for dealing with serious sui thoughts. This plan would include a safe person to talk to and/or go stay with. It may or may not involve your T, depending on how T handles things. I would discuss this plan with T so that you are prepared.

I listen on a suicide hotline. I have listened for five and a half years, many hundreds of hours, and I have contacted the Police a grand total of three times. Our particular office contacts the Police as a very last resort in times of extreme and immediate danger--and that's it.