My T is also CBT. He also has done that same guided imagery with going into my bedroom as a child and offering protection to my younger alter who held some of those bad memories. It is so wonderful your T asked for permission to go into that space with you. It sounds like your T is very considerate. They go with us in the imagery because they want us to know we are not going back into the memory alone. We were alone (usually) when trauma happened. This allows us to have the memory brought forward but in a safer way with a protector beside us. And then we offer comfort to that part of us which holds the memory and is stuck in that room at night.

Remember your T is on your side. You are not alone in what you have to process through. Talk through all the emotions with your T. By being a male energy in the visual room with you, it may have triggered you too much and you may not have felt like you had the voice or authority to tell him "no" even when he asked permission. I mean, when a child has a father "ask" to come into the room, is there ever an option to say "no" if the father is a perp?

Go over everything and make notes about your response. Then bring it up with T. Every single feeling you have around this is valid. And your T wants to know about it.