Its different for every couple, girl. In a perfect world, you both would know exactly when the time is right. Unfortunately, some people get attached faster than others and the person on the receiving end doesn't always see it coming. I don't think I would personally "freak" out, but that would be an awkward situation for me/anyone to be in.
I do think its possible for the two to feel it, but not have expressed it. Its a risk you take.