Well, nothing. What can you do after all? All you have left now are the memories, and the regret of not having appreciated what you had as much as you should have. You stand at the beginning of another cycle, another phase of your life, where you can't stop looking back and remembering the peaks and the troughs of the previous one, and the familiarity and stability you had established. But the worst part is, who can you even blame now? Isn't this exactly what you wanted? Isn't this what you've been working towards, preparing yourself mentally for? Isn't this what you looked forward to? How can you say now, that it's because of someone else's decision that you are where you are now, when you have yourself been waiting for this moment for a long time? Well, you cannot, this is what you wished for and this is what you have to live with.
So what now? Once you are in this situation, what's the step forward? For one, there's no looking back. You are where you are, and the only way to cope is to chin up and deal with it. If this is something that you wanted so badly, there were probably reasons for it. Finding those reasons is the key now. Remember why, in the first place, had you wanted to be here, and keeping those reasons in mind, move forward and find new reasons. Your life that once was, is not anymore, but there is another one waiting. New experiences, new challenges, new relationships waiting to be formed. How bad can it really be? You've done it before, you can do it again..
Anyway, one thing though, is quite clear. Always be careful of what you wish for, it might actually come true!