So sorry this is happening to you. So many people do not understand SI if they've never done it. Some people think that it is a suicidal thing. If your therp has known before that you did it, can you maybe talk to him/her and see if they can explain it to him? May not help but...

If your therp did not know of it until now, I wish you luck. But maybe it will be freeing to talk to that person. I used to be very ashamed but thanks to my therp I was constantly told it was a coping mechanism and that it was okay. That I was going to need to learn other ways to cope. Am I successful. I don't know that. I haven't SI'd since July, and I've been able to cope when triggered a couple of times. But I can't say that I won't do it again. One day at a time.
Good luck.