multiplicity_archives | Part of a system I am

Well.. hi there. I'm new to the community. I've been multiple for a long time, I've known about it for 3 years, and it has been only 15 days I can put a word on what I DO ACTUALLY have. MPD or DID doesn't sound too good when you know the definition of the disorders.
There's only someone else in my system. Same gender ( both of us are girls in a girl body, that helps), about same age, same specie, same tastes, but different behaviour and different thinking. Her name is Jessica. You can use my username to call me.
I've read about multiplicity, but I still have some questions.

First: what is a trigger?
Second: you've noticed I don't speak first person plural, that's because I am the only one "fronting" 99,9% of the time, and also because I'm aware of myself and of the other one, while she's not really( she discovered not so long ago she wasn't alone in this body, while I had known for a long time she was here)... you do the maths: she's still a bit freaked out. Has this ever happened to you?
Third( the last one for today, I promise): we don't like each other too much( but I can't imagine living without her, as she's kinda living through my actings). Are you "friend" with everyone in your system, or does this kind of thing happens?

There's more, but I don't feel like asking about the rest now.
I'm greeting everyone from everyone's system! Alas, I don't think you should expect a comment from Jessica.