How do you know he's the one?

My boyfriend and I are both 20, and we've been together for about a year. We go to different colleges, but try to see each other on weekends. We haven't had sex yet, (in fact, I'm still a virgin) but recently he told me that he wants to spend the rest of his life with me. I've only dated a few guys before him, but I feel the same way about him.  We want to wait until we're both out of college and financially stable before marriage, so we're in no hurry, but I was just wondering, how did you ladies know your husband was the one?