It really depends on a girl. What's she like, how she was raised, is she naive, is she a virgin, all that and more. It also depends on your timing and the situation.
I sweet talked my girl out of considering a breakup earlier today by telling her how I felt about her. But I took into account that she wanted a breakup BECAUSE she didn't know how I felt about her, and that we've been together for over a year. Thus, I said some things I would have never said to a fb/short term material.