I will also say, take the good answers with you and forget the rest. To me you made perfect sense the first time. To me, you explained this as well as it "can" be explained. I know for fact these entities sometimes exist in people, especially those who had a rough time. People have called them different things at different times, and maybe you don't like the word alter because it sounds like something the entity is not to you. These days people more call them parts, but you don't have to like that word either. If you like the word entity, we say that and that is totally fine.

I agree you don't sound psychotic. I understand you feel bad for someone to assume a lot and project things onto you. I would do too. But sometimes people (in general too) cannot get out of how they themselves experienced something so they think if someone else's experience is not identical, it is not valid. Those people haven't come very far in understanding others and they need to mature. While we cannot make them change, we can choose to ignore them, because if you explain something well and someone doesn't get it, it is not your fault. You did your best. If I don't get something, I'd rather ask than assume, sometimes I am caught assuming and then I feel very embarrassed. Most people don't mind being asked if there is something not understood. People do usually mind if others project things onto them. It's a normal reaction to feel bad about "told" how you are (Actually for me it is one of my biggest triggers, that people claim they know me better than I know myself).

Blah blah sorry about talking so much about myself. Anyway...

If you talk to professionals (good ones), sure there will be things said on your charts. But also, that is in a health care situation, everything you are diagnosed with does not have to be shared with others. I have only shared my diagnoses with a very few IRL. It might be that you will improve your life with Lyall. It also might happen since you are so open to his needs, that you will absorb him at some point. With the mind so many things are possible. It is your choice if you want to bring this up with a doctor/therapist. No one can force you to. No one can promise things will be better if you do. Life is full of choices and that is pretty scary a lot of times...