My significant other came out to me as trans last night

We have been dating for just over a year now and my “girlfriend” came out to me as trans last night (ftm). “She” was the first girl I’ve ever dated and getting used to a gay relationship was something I had to get used to and I realize this is too. We had a long conversation about how they feels and what they need and want from me in this. They are not ready to come out to anyone else, how do I talk to others about my -boyfriend- when they’re not ready for anyone else to know but still respect they’re preferences. This is all something I still need to wrap my head around and I just need all the advice from people who have experienced both sides of a situation like this. I just want them to be happy and comfortable.