To strongly crave or desire something is to long for it. No matter how healthful your diet is, you'll still occasionally long for chocolate, cookies, and cake.
The adjective long describes something that stretches over a large distance. If you're trying to avoid a prolonged visit with your crazy Aunt Martha, you might decide to take the long way to her house. The adjective long also describes something that lasts for an extended amount of time. When your Aunt Martha comes to your house, a half-hour can seem like a long, long time.