I've only been in love once, and it was absolutely instantaneous. Even to this day, I can remember exactly when it happened, what I was doing and what he was doing. In fact, I still have lingering feelings for him... and this was 8 years ago
I dated a different man for 6 years and was never truly in love with him, though I tried to force myself to be.
I have a very good friend who falls in love every night with a different guy. She says she loves love and will never settle down because of it. I suppose everyone is somewhere different on the love scale.