Well, this is a tough one. As difficult as it may be now, I would discuss it openly with him and be as accepting as possible of how each other feels. In this way, you can both share about how this was a surprise, and yet still something that you both "someday" wanted. Of course, there are tons of factors in your relationship that we don't know about, so this may not work for you, butit's how I'd approach it. Best of luck and blessings to all tree of you.