The "One"

They (whoever they are) say that when you meet the right one, you just know. What does this even mean? It wasn't love at first sight with Tom. It took awhile to decide if I wanted to get serious with him. And we dated 4 years before we got engaged...and I still have days where I question if we're making the right decision. I do love him, but marriage is supposed to be forever...and that's scary. We're both from divorced families. We're both still in our 20's and we already have multiple friends who were married, and divorced already. And I'm scared. I really want to get married once, and only once. So how do you make it work against all odds? How are you sure you're making the right decision? I guess it's "blind faith" because nobody ever knows 100% about it, you just make it work somehow. That terrifies me. The unknown...

Any advice? How do you "just know" that someone is the right person for you? And any tips on making a marriage work forever?

(Nothing happened to make me feel this way. I've been semi-nervous about marriage forever.)