My answer is going to be a little different than the others so far, because I don't believe in "soul mates" or "the one". It's not meant to sound pessimistic, but rather more realistic (which I know to some can be interchangeable, ha). I just don't think that out of the millions of guys on the planet who are in my age range and who are Christians that there is only one that I'd be compatible with for marriage.
I think it's more about a commitment than "Is he the one?" That makes me sound rather cold, as I do think love, understanding, etc. all need to be involved. But let's say that I'm dating someone who I think is "the one". We get married. He doesn't like kittens, he only tolerates mine, but it's whatever because I still love him. One week after we're married, I meet a guy who is everything that my husband is BUT he also likes kittens! What if he was actually "the one"?? That's just one example of why I think "the one" is a bit of a fantasy.
I'm not saying you have to commit to one person and then you're done because you've committed to them (not in regards to dating, at least; In marriage, most definitely it is to one person). Like Liamson said, time will tell. As you spend more time with someone, and time in prayer, you'll see what kind of person they are and whether that is someone you can be with for the rest of your life.