Pop the Question
It seems congratulations are in order! Perhaps that's a weird thing to say, actually, but you sound certain and happy and excited. And hey, what a long and complicated journey it is to come into our own gender as you are doing. So brava and good luck! As a mentor of mine used to say, it will probably be like going ass-first through a knothole, so that can't be all that comfortable. But then you'll POP! out to the other side and stop squeezing and be in a way better place.
About telling your friends. There are two things to deal with here: a) that you kept this from them, about which they might feel a bit betrayed; b) the actual news of your transitioning. If it were me, I would ease them into this a bit. Start picking their brains about what they know about trans concepts and stories. Maybe you could pick up Jennifer Finney Boylan's book She's Not There: A Life in Two Genders or Helen Boyd's She's Not the Man I Married: My Life with a Transgender Husband
and bring it up to them. "So I've been reading this book ... " Explain the basic premise, then just be quiet and let them talk. Let them tell you what they know about transitioning. Let them ask questions if they want to; let them expose their own thoughts to you. This might give you a better idea of where they stand, which will make it easier for you to reveal your own transition to them.
Then comes the issue that you kept this from your close friends. Do tell them—they will help you through this, but you might have to reveal why you haven't shared it with them yet. Tell them the truth: you haven't really shared this with anybody. It's been something you've gone through alone, thus far, but you don't want it to be in the future. You love them and care for them and value their friendship deeply, which is why you want to tell them what you're going (to go) through.
Separate these two things, a little, and perhaps think of it as two conversations, though they might happen simultaneously. They might be hurt at what they perceive to be your keeping something important from them, but as you are honest and explain why, they will realize that you need their support and are telling them now because you trust and care for them. So just lay it out: this is who you are, this is how you understand yourself, this is where you're going. It's a hard journey upon which you're embarking, but it'll be worth it.












