Hi Debbie! First of all, even the fact that you are open about this and only want the best for him is very sweet and I'm sure it means a lot to him. As has been mentioned, gender identity is not the same thing as sexuality- but that is a very common mistake to make, for those not in the LGBT community.

Now you know.

There is another mother here of a female-to-male young son, who has posted quite a bit about her son's journey. You can find her intro post here:
https://www.susans.org/forums/index.php/topic,39340.msg256597.html#msg256597And then if you click her username, you can read her posts. If you look through the rest of this SO forum, you'll also find that she's made some topics, just talking about some things her son experienced, how she's been coping with it herself, and even a trip they both made recently to a national convention. She hasn't been here in a little while, but I'm sure she wouldn't mind hearing from you if you want to chat.

Anyway, I would say right now, calling him by the pronouns he prefers will be a very good indicator to him that you're supportive. It's okay to slip up once in a while, just by force of habit you're used to saying 'her, she' etc. But if you make the effort, that's what counts.

And then it'll start to form a new habit and before you know it, you'll feel like he was always your son all along.
Welcome to Susan's, I hope you like it here and find it informative and helpful.