Just cut off a friend then found out her ex will join my rehab

I am so FUCKING pissed. I just wanna vent my feelings. Basically,I am in a healthy relationship with my boyfriend,and I love him to bits. I have this friend. Let's call her S. I called S when I was splitting this Sunday,wanting support,then she began telling me that my boyfriend does not actually love me and that I should leave him. She states my exact fears back to me. I was not thinking clealx,so I did as she said. Luckily,my boyfriend is amazing and a couple hours later,when I texted him,having calmed down and began apologizing,he understood the situation and was not mad at me.

I met with this friend yesterday. She kept repeating the same things,and I felt so sick, I had to get back from my outing earlier. She even treathened to tell my boyfriend what I told her when I was splitting. So I cut her off. And today,I find out that her ex,whom she is still in contact, and is good friends with, is on the waiting list.

I feel so furious. I am afraid that if she joins, the safety that I experience in group therapy will be tempered with. I fear that N,this girl,will tell S about the things I say in group therapy. I am furious, because I feel like this is my only chance to heal and it is like it is being taken away from me. I do not know what to do. I will try to speak with my handler about this.