I may be way off the mark here, but I have been and continue to be close with people who are multiples and they use this exact phrase "someone in there" and have disagreements among alters about who is telling the truth about what kind of experiences.

But it seems like I'm the only one who may think you are talking about an alter as opposed to talking about another client that your T sees who has given you fits in the past. But I don't want to really go down this road and talk about the difficulties that T's face treating multiples, especially when certain alters start talking after long periods of time of silence.

If this is about the same person who has caused trouble before with your T (although it is really him who caused the trouble), I am just sorry, and sorrowful that you have to go through this.