How do you feel about your T? You mentioned them sounding sharp, do you feel safe and comfortable with them? Or to go a bit further do they seem caring and kind toward you?

From what you describe and from my entirely non-expert knowledge it seems like something akin to DID is possible (I think it's all on a spectrum-- dissociation is a coping mechanism for many). But if you have children in your system (as would be probable with DID I believe?) it doesn't seem likely they'd come forward if your T is "particularly serious and rather sharp" with you.

Do you remember much from childhood?