Do you regret only being with 1 person??

Have you ever only been with (and are still with) only 1 person? Do you regret your relationship? 
I've been with my bf for almost 3 years. I can't even begin to describe how much I love and cherish him, he means the world to me. But I've been with him since end of sophomore highschool till now (college freshman) with every fiber of my being I can't imagine ever breaking up with him. I know I don't want anyone else. But then again, how do I know if I don't want anything else if he's all I've ever known?  Ya know?