Hi Lizzy,
I am so sorry to hear this happened. Although you say that he didn't force you and that you wanted it to happen at the time, he was still in a powerful position and you were the vulnerable one coming to him for help and from that aspect, it is still very much abuse and you have every right to feel as upset as you do.
I am glad that he has been deregistered but that doesn't stop your pain and the pain of unfortunately we don't know how many more. He took advantage of someone in need of closeness.
I think you have been incredibly brave to seek therapy again and I hope that once you can build up some level of trust that they will be able to help you. As with any situation, therapy doesn't make it instantly better, so sometimes there is a low before we come out of it which may explain why you arent feeling better with therapy.
It is going to be hard also as being in therapy may be triggering but I hope you can get the help you need.