Beyond Blue,
Reading this makes me feel so much because I know I have felt such similar confusion and dismay. So I first want to tell you that although your feelings are unique to you, many others have felt similarly, and have been able to feel better, much better, at later points.
If this is the first T you have ever been able to open up to, I think you are wise to trust yourself, and trust your T to help you. You do not have to accept this diagnosis, but you would be very brave to try exploring it, and see if doing so may help you.
The fear of recovering "false memories" is something that I have struggled with as well. It is very scary. For me, I actually did construct suggestions for myself that were not true. But I found that at least part of me knew when I was lying to myself. When I uncovered things that really were true, I knew that too. This is not an easy trek to embark on, but for me it was worthwhile.
You state that you don't want to lose the wonderful memories of your childhood. I would like to say to this that you don't have to lose any of the good stuff. You may uncover other things that were hurtful, but you can still treasure all the things that were good in your childhood. I found it necessary for me, at one point, to decide if it was more important to remember being happy in the past, or to have a chance at being happy now and in the future? That helped me decide to be more willing to explore past experiences that I was afraid of.
You are asking some very good, thoughtful questions about the nature of any distinct personalities you might have. Such as How could I have been unaware of them? There are many possibilities, and the answers are going to be different for everyone. I am still trying to answer some of them myself. But I can see you are thinking on them, you are considering them, and that is the path to finding the answers. I hope you will continue to ask all of these questions of yourself and your T.
It is completely reasonable and understandable that you would feel you are falling apart right now. It is perfectly okay to feel that way. You will be very brave, and taking very good care of yourself, if you continue to explore the possibility of DID, whether you conclude it describes you or not.
I want to echo the others in hoping you can be gentle with yourself. You are a worthwhile person who deserves to be happy, by whatever path leads you there.
Thank you so much for sharing this with us. I hope to hear more from you.