If you are talking about a way to get two future lovers to meet each other, a good catalyst might be to have the girl in a situation where the boy has to be her rescuer.
This doesn’t have to be any kind of life-or-death deal, of course, but just something as innocuous as:
1. Her kitten is up a tree, and he climbs up and gets it for her.
2. She has locked her keys in her car, and he uses a coat hanger to get inside the car.
3. She has a flat tire, and he changes it for her.
4. She’s walking home carrying too many bags of groceries. She drops them and he offers to help her with them.
5. They happen to be at the same store at the same time, and she doesn’t have enough money to pay for all of her purchases. He makes up the difference for her.
6. Some dude is bothering the girl, so the boy walks over and says, “Everything OK, Sis?” She picks up on that, and she walks away with “her brother.”
7. She steps off a curb and into the path of an oncoming car that she did not see. He is there and grabs her arm, pulling her back to the curb, saving her life.
Perhaps those will give you other ideas, as well. The idea is that it needs to be an incident which makes her want to get to know the boy, a little better, because he did something significant for her, in her life.