The reason for the letters is to include all the non-hetero, non-cis people for the sake of conversation, as people who may have experienced institutional discrimination or had to hide their identities due to societal expectations.
I, personally, don’t consider myself “part of the community”, though I tend to fall in the asexual spectrum (the Google term, if you’re interested, is demisexual) and do not consider gender or biological sex a factor in determining whether I find someone attractive. I’m attracted to intelligent people with strong personalities. Since I am married and in a monogamous hetero relationship, I do not experience the discrimination that others in the LGBTQAI community do.
Even within “the community” there is in-fighting and discrimination. It’s a huge thing.
The biggest thing to remember is that while it’s convenient to refer to “LGBTQAI issues” the community is made up of individuals, and those individuals cannot be swept into their “letter” neatly. Some bisexual or pansexual people will choose to never enter into a committed relationship. Others can’t wait to pick out wedding clothes. Some trans* people are gay and some are straight and some are bisexual or pansexual. Some gay people are polyamorous and some are firmly monogamous.
I cannot imagine why you’d ask about separating gay people from bisexual and trans* folk, unless it was under the mistaken impression that bisexual, pansexual, and gender-nonconforming people, as a whole, prefer not to be in a committed relationship.
I hope that’s been cleared up for you.