How'd you know you're in love?

"Love is a basic dimension of human experience that is variously conveyed as a sense of tender affection, an intense attraction, the foundation of intimacy and good interpersonal chemistry, willing self-sacrifice on behalf of another, and as an ineffable sense of affinity or connection to nature, other living beings, or even that which is unseen. It manifests itself in feelings, emotion, behavior, thoughts, perception and attitude. It influences, underlies and defines major patterns in interpersonal relationships and self-identification."

How do you make it sure, it's that certain special feeling or it isn't just an infatuation?