How do you know your love will last forever?

I have an amazing BF who I've been with for about a year now. He knows me better than myself. He makes me feel beautiful and important and promises me the world, I know I want him as my husband. But sometimes I feel like I can't love him enough, like I'm scared I won't keep him happy forever even though he promises I will. Is this a normal feeling? Should I be worried? What can I do?