
http://www.mangago.zone/read-manga/courting_a_prince/mdx/iur_chapter-5/pg-4/
The feeling is mutual for me. Once I entered high school, I became closer to my friends and they offered me something and I was hesitant to take it, I looked around and said "you were talking to me?" ╥﹏╥
Don'the worry, I got myself friends that I could kinda talk to now. I'm improving and gaining courage to talk to others.

DID occurs when someone has experience a traumatic event. The body splits itself in order to protect the harmed person.
A representation will be like if a glass bowl shattered to pieces; there is no owner. Its like saying which shattered piece is the original. So its rude to say who is the original owner of the body to someone who has DID.
Each individual comes with their own personality and memories that the others dont have.
Ask questions if you are curious. Im knowledgable to help you answer them (=・ω・=)

They are there own selves and each develop memories.
Amnesia also plays a big part toward DID. When the host, the person who is out the most, switches the person gets amnesia and does not remember what the alters, the individuals inside the body, are doing.
This causes a problem since the smallest thing could trigger a switch. Such as one of the alters favorite thing. Its a problem because there are also children present which are called littles. When littles are incharge of the body they could be doing something, such as wondering around, that will lead them to danger. They are just children and dont know what they are doing.
The alters may vary to men, women, nonbionary, and so on. When you meet someone with DID dont act weird and dont be afraid.

Is the "switch" between personalities really involuntarily? Can it be controlled? Like, can some learn to control it? And what about during important stuff like sex. What happens to the person with DID when switching personalities during sex. Specifically a personality that's not being intimate with anyone.
What happens then?

It is mostly involuntary. There are positive and negative "triggers". So you could say switching can be controlled. But it would be extremely rude to trigger someone with DID just because you want to talk with another identity from the "system". I recommend multiple channels on youtube, like Multiplicity and Me.

1. Yes, its involuntarily.
2. They cannot be controlled and its rude to show an object a alter enjoys to force them out.
3. Most likely a switch will not happen due to the alter seeing something they like that prevents them to switch. If a switch happens the significant other must stop all actions and cover the person or the alters may not allow sex. It depends on the people.
I dont really have much knowledge of the topic of intimacy so hope this helps
Its funny how mostly everyone read this when we were young. probably that's why we feel so attached to this. This, sadly, doesn't have an anime but I'm worried if it does, it wouldn't be as good. It's more mysterious when you are reading it.