You need to talk to him as soon as you get the chance and let him know the situation.  And from there, you really need to discuss and decide what you want to do about it.  Sitting here and wondering how he will respond will get you no where.  And waiting won't change things or make the pregnancy go away.

So while it may be scary, just sit him down, and tell him you have to talk about something important.  And then let him know.  From there, it's up to both of you to discuss what you want to do.