how would you know that he or she is 'the one'

Honestly, with me and my DH it was a given. We had been together since we were very small so it was just a natural progression with us. But, I think the most important things were that we wanted the exact same things in life. We had our priorities in the same places. We agreed that we wanted to finish our degrees, we agreed on children, money, religion, and other important aspects we would be dealing with daily. We also made each other laugh, enjoyed each other's company, and finished each other's sentences. I think it is vital that a lot of the day-to-day issues have to be resolved before getting into a marriage. How will you deal with finances? How many children (if any) do you want? How will you handle family and friends after marriage? Getting this all out and agreed with prior to marriage will make "all eternity" so much nicer!