That's a good question...
Maybe it's got something to do with karma?

In my case it started out as just really liking the guy. Then we became closer and I found that I not only really liked him, but I felt safe and warm when we were together and I could tell him anything. Then I found myself missing him when we weren't together and then when we had that first kiss I knew it. Plus the way he smells and just gets me helped too. You know just little things. ^_^