I'm a 29-year-old guy with a "keep it casual" relationship history, but I can't stop thinking about this new girl at work. Beyond not wanting her to date anyone else, I don't want someone to hurt her or make her sad. No other woman has ever made me feel this way. How do I know whether this is lust or the beginnings of falling in love?

It's easy to believe you're "in love" when you're really just in lust. To be fair, lust is a form of love...if you broaden the field to stuff like "I...