Hello Romex: So I take it you came out to your mom about being bi, but not trans. And all of your relationships are with trans guys, which your mom disapproves of. I don't know as I have any great suggestions, or insights, to share with you here. But perhaps it's like an old "Peanuts" poster I recall from years ago. The caption on it said: "I love humanity. It's people I can't stand." Perhaps your mom is accepting of LGBT people in theory. But she doesn't want you to have anything to do with them in reality.

Another possibility here is that being bi doesn't require a person to make any physical changes. Being trans however suggests the possibility that, at some point, you might change your physical appearance... perhaps even have hormone replacement therapy & surgery. And your mom is concerned that hanging with trans guys may influence you to want to do some, or all, of those things.

I know that hiding your real self, if you are truly trans (are you sure?) can be excruciatingly difficult. However, you have to protect yourself as well. So perhaps, given your situation, keeping your gender identity a secret from your mom is for the best, if that's something you feel you can do. This will also buy you time to really decide if you really are trans.

Right now, it sounds like, your friends are primarily trans guys. So that does perhaps have some influence on you. Once you get to college & get to know other people, have different experiences, etc. it's possible your perspective could change. After all, being trans isn't black-&-white... you either are or you're not. There are many resting places along the gender identity & sexual orientation continuums. And each of us has to decide, in our own minds where we come to rest. I wish you well...