How Do I KNOW?

Excuse me while I think out loud...

How do you know if he is the one? I am in a relationship right now in which I THINK he is the one. But sometimes I wonder. How am I supposed to know if in 50 years he will still be the man for me? In the last couple years I have learned so many things about him - some I love, some I deal with, but overall he is a great man. We have a great time together. We watch movies, take walks on the beach, work out together, have family dinners together, vacation, have deep conversations, pray together, read in bed at night together, talk about our future. I can see myself looking into his face and saying 'I do.'
The more I think about I do, the more scared I get. I was in a loooong relationship before him that was disastrous. He was a complete self centered, narcissistic, manipulative jerk. He was fun, hilarious, and a great lover - but that was it. He messed up my world. After him, I thought I'd never trust or love again. For years after I finally wiped my hands clean of him, I dated a lot, but never opened up. Until I met my babe. He changed everything, he made love easy.
Now, I'm having second doubts. How can I know he will be faithful to me? After all, he is just a man! How can I really put so much trust into ONE person? I feel so vulnerable and naked, lately I've been bursting into tears just thinking about getting my heart broken - and for no real reason! What the hell is up? Thoughts?

PMS?

Peace