You have to create as many love as possible: when you go very close to other you feel the love, and when more people loves you, you'll earn more points. When a person is full of love his heart goes golden, and when you have converted a certain amount of hearts to golden you pass to the next level. However, if you run out of love before doing it, you lose. During the game you'll find positive and negative bonuses. For example, the hot dogs turn the little pig introspective and self-reflective, something not very good for love; in contrast, the corn enable him to move faster, something very helpful. So it depends on the case if you should collect or not a given bonus.
You have to create all the love you can: when you are close to another you feel the love, and when many persons love you at the same time you eran more points.