A couple of times, but the first two times it was more of a passion-based thing as opposed to a true compatibility, last-a-long-time type of thing.
The first time was when I was 14. I fell in love with my boyfriend who was 16. We broke up because he ended up leading a very...rough life.
He still is, last I heard a few years ago.
I fell in love for the second time last spring...but it was un-reciprocated. That was extremely crushing, but now looking back on it, it's a darn good thing we didn't stay together. He showed himself to be very cold and unemotional. I would've been miserable.
I'm in love right now, and he loves me just as much. We've been dating for over 5 months, and so far it's been absolutely lovely. We have even talked about future plans and things. I really don't want to say too much because I don't want to jinx the relationship, but so far it feels like a really good thing for me.
When you do fall in love genuinely...you just know it. I know it sounds cliche, but it is extremely true. You really don't have to question it, you just know it's something big.