Scarlet, I am so sorry your trust has been broken. No matter how it happens, it is a horrific place to be. I am glad you talked about it and I hope you can keep talking about it. As another said, this may help, it may not.

I can relate, a little, because the way my T has handled this ending between us is downright outrageous in my opinion. For me, and I wonder if for you, it feels like it has destroyed everything that went before it. All gone, in a heartbeat.
I decided to write. Write and write and write and write. I sent her 4 emails in a day. I went through all the thought processes and emotions possible in those emails I think. Does writing help you to process?

The other thing I did which was actually really helpful was to write all of the good that she has done. All of the good that we have done. All of the things we have been though and that we have survived. It helped me to see that this is one incident. Same for you. Whilst it feels ABSOLUTELY ENOURMOUS and totally insurmountable, it is, at the end of the day, one incident. One mistake. A f***king HUGE mistake, which should never have happened and which you have every right to be angry about, but she is human, same as all of us. And if you want to try and heal the hurt, you have to try and find ways, which you are doing by asking for suggestions.

So, not sure if it will help or not, but do keep telling her how you feel. Do keep talking about it (and feel and express the anger at now having to waste sessions talking about something SHE did! - I've been there a few times in the last 5 years as well!)
And maybe write about it. Grab a notebook and a pen and just pour out everything that is in your mind. And maybe try the exercise that helped me. Write out everything good that she has done. All the kind, helpful, considerate, supportive things. Write out all the positive changes you have made to your life as a result of your therapy.

And take good care of yourself as you go through this hell. Hopefully others will also have some suggestions and something will click for you, in time.

Thinking of you...