Most likely the girl will either say it first, or she will give a hint as to what shes thinking. If you ever get into a conversation about love be like "You have no idea how much I care for you" and depending on her response, keep insisting that you care more. If she says back "you'd be suprised" or "No, I defenately win this one" or something along those lines, be like "theres a fine line between loving someone, and being in love with them..." and continue from there.

GOOD LUCK!