Hon, you don't sound stupid - we're all emotional, fragile people, as strong as we might appear to the people around us. Besides this huge change we are going through with all the anxiety and uncertainty and everything associated with it, most of the very people we need to support us at such a time abandon us instead, AND then there's still all the hormonal changes and things happening. You're not stupid. You're an unbelievably brave, strong individual who has taken a life that was all wrong, and you have started to turn it into what it was meant to be. Very few people can say that.
AS to your boyfriend - What he did to you was very wrong. How can he spring something like that on you in front of everybody - before he had spoken to you about it?!?! How selfish a gesture. Whether you are trans or not, ask yourself if that is the basis for a healthy relationship.
Add to that his homophobia and stuff, and well, just think about it.
Perhaps he's given you a way out though. You could confront him on this, explain that you were hurt and surprised by the proposal, and say that you need time to consider it carefully, because it is such a big commitment to make. Explain that some time away from each other - him in the army, you in London, could be just what you both need to get some perspective on the relationship. It's an easier let-off than breaking up with him and him demanding reasons, and then, once in London, you can send him a letter or phone him and break it off from a safe distance - I know that sounds selfish, but you need to look after your own safety first.
Good luck dearest.
Simone
