I don't really agree with this, it just sounds like mind games and PUA tactics. OP, as long as you're showing interest and putting in effort, it'll work out. Don't follow advice, ie "Start seeing other girls" to have that abundance mentality. That's complete bullshit, and it'll be really obvious to the girl and ruin things. When it gets sexual too fast, it's really easy for cognitive dissonance to creep in, and it'll be hard for you to detach if things do turn to shit.

Since, we're both 25, I'd say, "Hey, I really see this working out, and love getting to know you. I'm not seeing anyone else, since I really enjoy our time together." Then, the ball ja in her court :)