When I first read this question my reaction was that no, love isn't the only thing that inspires literature. However the more I thought about it, the more I realized how it does influence each story. However if you want to get specific, I don't think that romantic love inspires literature more than anything else, but rather a love of anything. Writer's have to love something while writing a story because literature requires so much work to see through to completion. And because it doesn't guarantee success, it will always be a labor of love. Maybe you love nature and that inspires you to write a story, or maybe you love your friends and that produces a story. Love may seem like a narrow category when you think of it as a genre (these books are about love) but if you really stop to think about it, love is kind of a blanket term that can apply in a variety of ways to almost any story.