How do you know that no one else will ever love you that deeply again?
Do both of you a favour and get real with your feelings. If you're not feeling it then tell her, but think about it. Don't be a dumba** and throw it all away.
Plus, if she truly loves you then she'll want you to be happy. It's a pretty selfless thought, but it's true.
And don't you think that she deserves for someone to love her like she does you? Think about it.

Everyone has doubts. It's human nature. Deal. Relationships are hard work and really it's a matter of how much work you want to put into making it last.

We all wish that we could "just know". We may feel certain and absolutely sure that they are "the one" and then they break your heart.