As someone who has seen how damaging involuntary hospitalization can be, my advice is not to tell your therapist. I try to see every decision as a risk:reward ratio. The risk? You might get committed. The reward? You might feel a little better if you talk about it. (I never do, but some people apparently are relieved when they talk about what's troubling them.)
When I look at that ratio, it seems to me that the risk clearly outweighs the possible reward. You should make your own evaluation of whether it's worth it.
Edit: Several people have said that good therapists understand the difference between plans and ideation, but the fact is that many therapists are bad at their jobs. Since you are just starting to get to know this one, you don't know whether he/she can be trusted yet.
When I look at that ratio, it seems to me that the risk clearly outweighs the possible reward. You should make your own evaluation of whether it's worth it.
Edit: Several people have said that good therapists understand the difference between plans and ideation, but the fact is that many therapists are bad at their jobs. Since you are just starting to get to know this one, you don't know whether he/she can be trusted yet.